Laser irradiation method and method of manufacturing a semiconductor device

ABSTRACT

A method of manufacturing a semiconductor device is provided which uses a laser crystallization method capable of increasing substrate processing efficiency. An island-like semiconductor film including one or more islands is formed by patterning (sub-island). The sub-island is then irradiated with laser light to improve its crystallinity, and thereafter patterned to form an island. From pattern information of a sub-island, a laser light scanning path on a substrate is determined such that at least the sub-island is irradiated with laser light. In other words, the present invention runs laser light so as to obtain at least the minimum degree of crystallization of a portion that has to be crystallized, instead of irradiating the entire substrate with laser light.

This application is a Divisional of Ser. No. 10/314,452 Filed Dec. 9,2002 now U.S. Pat. No. 7,214,573.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a laser irradiation method forcrystallizing a semiconductor film using a laser light or for performingactivation after ion implantation and to a method of manufacturing asemiconductor device.

2. Description of the Related Art

In recent years, a technique of forming a TFT on a substrate has greatlyprogressed, and its application and development for active matrixsemiconductor display devices have been advanced. In particular, since aTFT using a polycrystalline semiconductor film has higher field-effectmobility (also referred to as mobility) than a TFT using a conventionalamorphous semiconductor film, it enables high-speed operation. Althoughthe pixel is conventionally controlled by a driving circuit providedoutside the substrate, it is therefore possible to control the pixel bythe driving circuit formed on the same substrate where the pixel isformed.

Incidentally, as for the substrate used in the semiconductor device, aglass substrate is regarded as promising in comparison with a singlecrystal silicon substrate in terms of the cost. A glass substrate isinferior in heat resistance and is easily subjected to thermaldeformation. Therefore, in the case where a polysilicon TFT is formed onthe glass substrate, in order to avoid thermal deformation of the glasssubstrate, the use of laser annealing for crystallization of thesemiconductor film is extremely effective.

Characteristics of laser annealing are as follows: it can greatly reducea processing time in comparison with an annealing method using radiationheating or conductive heating; and it hardly causes thermal damage tothe substrate by selectively and locally heating a semiconductor or thesemiconductor film, for example.

Note that the laser annealing method here indicates a technique ofre-crystallizing the damaged layer formed on the semiconductor substrateor the semiconductor film, and a technique of crystallizing thesemiconductor film formed on the substrate. Also, the laser annealingmethod here includes a technique applied to leveling or surfacereforming of the semiconductor substrate or the semiconductor film. Alaser oscillation apparatus applied thereto is a gas laser oscillationapparatus represented by an excimer laser or a solid laser oscillationapparatus represented by a YAG laser. It is known that the apparatusperforms crystallization by heating a surface layer of the semiconductorby irradiation of the laser light in an extremely short period of timeof about several tens of nanoseconds to several tens of microseconds.

Lasers are roughly divided into two types: pulse oscillation andcontinuous oscillation, according to an oscillation method. In the pulseoscillation laser, an output energy is relatively high, so that massproductivity can be increased by setting the size of a beam spot toseveral cm² or more. In particular, when the shape of the beam spot isprocessed using an optical system and made to be a linear shape of 10 cmor more in length, it is possible to efficiently perform irradiation ofthe laser light to the substrate and further enhance the massproductivity. Thus, for crystallization of the semiconductor film, theuse of a pulse oscillation laser is becoming mainstream.

However, in recent years, in crystallization of the semiconductor film,it is found that grain size of the crystal formed in the semiconductorfilm is larger in the case where the continuous wave laser is used thanthe case where the pulse oscillation laser is used. When the crystalgrain size in the semiconductor film becomes large, the mobility of theTFT formed using the semiconductor film becomes high. For this reason, acontinuous wave laser has been attracting attention recently.

However, since the maximum output energy of the continuous wave laser isgenerally small in comparison with that of the pulse oscillation laser,the size of the beam spot is as small as about 10⁻³ mm². Accordingly, inorder to perform processing on one large substrate, it is necessary tomove a beam irradiation position on the substrate upward and downward,and right and left, and the processing time per substrate is prolonged.As a result, the efficiency of substrate processing is poor and there isan important problem of how to improve the processing speed of thesubstrate.

Note that beam spot length adjustment technologies using a slit haveconventionally been used (refer to, for example, Patent Document 1 andPatent Document 2 below).

Further, technologies using a laser light of continuous oscillation forcrystallization after forming the semiconductor film into an islandshape have conventionally been used (refer to, for example Non-PatentDocument 1 below).

(Patent Document 1)

JP 11-354463 A (page 3, FIG. 3)

(Patent Document 2)

JP 09-270393 A (pages 3 to 4, FIG. 2)

(Non-Patent Document 1)

Akito Hara, Yasuyoshi Mishima, Tatsuya Kakehi, Fumiyo Takeuchi, MichikoTakei, Kenichi Yoshino, Katsuyuki Suga, Mitsuru Chida, and Nobuo Sasaki,Fujitsu Laboratories Ltd., “High Performance Poly-Si TFTs on a Glass bya Stable Scanning CW Laser Lateral Crystallization”, IEDM2001.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above problem, and anobject of the present invention is therefore to provide a laserirradiation method using a laser crystallization method that can raisethe substrate processing efficiency and mobility of a semiconductor filmfrom those of prior art and to provide a method of manufacturing asemiconductor device which uses the laser irradiation method.

The present invention uses shape data (pattern information) of a mask ofa semiconductor film to grasp which part of the semiconductor filmbecomes an island-like semiconductor film (island). Then, an island-likesemiconductor film that includes one or more of such islands is formedby patterning (sub-island). The sub-island is improved in crystallinityby laser light irradiation, and then patterned to form an island.

Furthermore, the present invention uses pattern information of asub-island to determine a laser light scanning path on a substrate sothat at least the sub-island is irradiated with laser light. In otherwords, the present invention runs laser light so as to obtain at leastthe minimum degree of crystallization of a portion that has to becrystallized, instead of irradiating the entire substrate with laserlight. With the above structure, time for laser irradiation of otherportions than a sub-island can be saved to shorten the whole laserirradiation time and improve the substrate processing speed. The abovestructure also makes it possible to avoid damage to a substrate which iscaused by irradiating a portion that does not need laser irradiationwith laser light.

In the present invention, a marker may be formed in advance on asubstrate by laser light or the like, or a marker and a sub-island maybe formed at the same time. By forming a marker and a sub-islandsimultaneously, one less marker mask is needed and the marker can bepositioned more accurately than when forming it by laser light tothereby improve the positioning accuracy. The present invention uses themarker as the reference and determines the laser light scanning positionbased on pattern information of the sub-island.

The present invention sets intentionally the laser light scanningdirection such that, as the beam spot reaches a sub-island while thesubstrate is scanned with laser light, one point of the beam spot comesinto contact with the sub-island viewed from the direction perpendicularto the substrate. For example, if a sub-island has a polygonal shapewhen viewed from above the substrate, laser light first runs in a mannerthat brings the beam spot into contact with one corner of thesub-island. If a part or the entire length of a sub-island is curvedwhen viewed from above the substrate, the laser light scanning directionis determined such that one point of the beam spot comes into contactwith the curved portion of the sub-island first. Laser light irradiationis started from the one contact point to commence growth of crystalshaving <100> orientation from the contact point and the vicinitythereof. The laser light scanning is continued until irradiation of thesub-island with laser light is finished. As a result, the <100>orientation ratio of the entire sub-island is improved.

When an island with a high <100> orientation ratio is used for an activelayer of a TFT, the TFT can have high mobility. An active layer having ahigh <100> orientation ratio can reduce fluctuation in film quality of agate insulating film formed thereon and accordingly can reducefluctuation in TFT threshold voltage.

When a sub-island is irradiated with laser light, microcrystals areundesirably formed in the vicinity of edges of the sub-island viewedfrom above the substrate. For instance, a large number of microcrystalshaving a grain size of less than 0.1 μm are found in the vicinity ofedges of a sub-island irradiated with a pulse oscillation excimer laserlight, although it depends on the thickness of a semiconductor film, andthe grain sizes of the microcrystals are smaller than the grain sizes ofcrystals formed in the center of the sub-island. This is supposedlybecause heat by laser light diffuses to the substrate differently in thevicinity of edges and in the center.

Therefore, the present invention removes, after laser lightcrystallization, portions in the vicinity of edges that have poorcrystallinity by patterning and uses the center of the sub-island thathas better crystallinity to form an island. Which part of a sub-islandis to be removed by patterning to form an island can be appropriatelydetermined at designer's discretion. The crystallinity of an island canbe enhanced more by crystallizing a sub-island with laser light and thenforming an island in this way instead of directly crystallizing anisland with laser light.

Furthermore, the present invention uses a slit to cut off a portion of abeam spot that is low in energy density. The use of a slit allows asub-island to receive irradiation by laser light of relatively uniformlaser energy density and the sub-island can be crystallized uniformly.Providing a slit also makes it possible to change the width of a part ofa beam spot in accordance with pattern information of a sub-island. Thisreduces restrictions in layout of a sub-island and an active layer of aTFT as well. The beam spot width means the length of a beam spot in thedirection perpendicular to the scanning direction.

Shapes of beam spots that can be used in the present invention includean ellipse, a rectangle, a line, and others.

One beam spot obtained by synthesizing laser lights that are emittedfrom plural laser oscillation apparatuses may be used in lasercrystallization. This structure allows low energy density portions oflaser lights to compensate one another.

After a semiconductor film is formed, or after a sub-island is formed,the semiconductor film may be crystallized by laser light irradiationwithout exposing the film to the air (rare gas, nitrogen, oxygen, orother specific gas atmosphere or a reduced pressure atmosphere isemployed). This structure can prevent molecule-level contaminants in aclean room, such as boron contained in a filter for enhancing thecleanliness of air, from mixing in the semiconductor film during laserlight crystallization.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A to 1D are diagrams showing a laser irradiation method of thepresent invention;

FIGS. 2A to 2D are diagrams showing a shape and energy densitydistribution of a laser beam;

FIGS. 3A and 3B are diagrams showing the energy density distribution ofa laser beam;

FIGS. 4A and 4B are diagrams showing the shape and energy densitydistribution of a laser beam;

FIGS. 5A and 5B are diagrams showing the laser beam shape and apositional relation between the laser beam and a sub-island;

FIGS. 6A to 6D are diagrams showing the positional relation between aportion irradiated with laser light and a mask;

FIGS. 7A and 7B are diagrams showing the positional relation between aportion irradiated with laser light and a mask;

FIGS. 8A and 8B are diagrams showing the positional relation between alaser light moving direction on a processing object and a mask;

FIGS. 9A and 9B are diagrams showing the positional relation between aportion irradiated with laser light and a mask;

FIG. 10 is a diagram of a laser irradiation apparatus;

FIG. 11 is a diagram of a laser irradiation apparatus;

FIG. 12 is a diagram showing production flow of the present invention;

FIG. 13 is a diagram showing the production flow of the presentinvention;

FIG. 14 is a diagram showing the production flow of the presentinvention;

FIG. 15 is a diagram showing the production flow of prior art;

FIGS. 16A and 16B are diagrams showing the positional relation between aslit and a beam spot;

FIGS. 17A to 17D are diagrams each showing an optical system of laserirradiation apparatus;

FIGS. 18A and 18B are diagrams showing the positional relation between aportion irradiated with laser light and a mask;

FIGS. 19A to 19D are diagrams showing directions of laser light movingon a processing object;

FIG. 20 is a diagram showing a direction of laser light moving on aprocessing object;

FIG. 21 is a diagram showing the energy density distribution in acentral axis direction of overlapping beam spots;

FIGS. 22A to 22C are diagrams showing how beam spots are overlapped;

FIGS. 23A to 23D are diagrams showing a method of manufacturing asemiconductor device which uses a laser irradiation method of thepresent invention;

FIGS. 24A to 24C are diagrams showing a method of manufacturing asemiconductor device which uses a laser irradiation method of thepresent invention;

FIGS. 25A to 25C are diagrams showing a method of manufacturing asemiconductor device which uses a laser irradiation method of thepresent invention;

FIG. 26 is a diagram showing a method of manufacturing a semiconductordevice which uses a laser irradiation method of the present invention;

FIG. 27 is a diagram of a liquid crystal display device manufactured byusing a laser irradiation method of the present invention;

FIGS. 28A and 28B are diagrams showing a method of manufacturing a lightemitting device which uses a laser irradiation method of the presentinvention;

FIG. 29 is a sectional view of a light emitting device using a laserirradiation method of the present invention;

FIG. 30 is a diagram showing the production flow of the presentinvention;

FIG. 31 is a diagram showing a method of manufacturing a light emittingdevice which uses a laser irradiation method of the present invention;

FIG. 32 is a diagram showing the production flow of the presentinvention;

FIG. 33 is a sectional view of a light emitting device using a laserirradiation method of the present invention;

FIGS. 34A to 34L are diagrams showing a method of manufacturing asemiconductor device which uses a laser irradiation method of thepresent invention;

FIGS. 35A to 35G are diagrams showing a method of manufacturing asemiconductor device which uses a laser irradiation method of thepresent invention;

FIGS. 36A to 36G are diagrams showing a method of manufacturing asemiconductor device which uses a laser irradiation method of thepresent invention;

FIGS. 37A to 37C are diagrams showing a method of manufacturing asemiconductor device which uses a laser irradiation method of thepresent invention;

FIG. 38 is a graph showing the energy difference in relation to thedistance between centers of beam spots;

FIG. 39 is a graph showing the output energy distribution in the centralaxis direction of a beam spot;

FIGS. 40A and 40B are diagrams of a panel with a driving circuit mountedthereto; and

FIG. 41 is a sectional view of a light emitting device manufactured byusing a laser apparatus of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment Mode

Descriptions will be given below on a laser irradiation method andsemiconductor device manufacturing method of the present invention withreference to FIGS. 1A to 1D.

First, as shown in FIG. 1A, a semiconductor film 11 is formed on asubstrate 10. The substrate 10 can be any material as long as it canwithstand the processing temperature in later steps. For example, aquartz substrate, silicon substrate, glass substrate, metal substrate,or stainless steel substrate with an insulating film formed on itssurface can be employed. The glass substrate is formed of bariumborosilicate glass, aluminoborosilicate glass, or the like. A plasticsubstrate may also be employed if it has enough heat resistance towithstand the processing temperature.

An insulating film is formed between the substrate 10 and thesemiconductor film 11 to serve as a base film for preventing an alkalinemetal or other impurities contained in the substrate 10 from enteringthe semiconductor film 11.

The semiconductor film 11 can be formed by a known method (sputtering,LPCVD, plasma CVD, or the like). The semiconductor film may be anamorphous semiconductor film, a microcrystalline semiconductor film, ora crystalline semiconductor film.

Next, the semiconductor film 11 is patterned as shown in FIG. 1B to forma sub-island (before laser crystallization (Pre-LC)) 12 and a marker 19.The shape of the marker is not limited to the one shown in FIG. 1B.

The sub-island (Pre-LC) 12 is then irradiated with laser light as shownin FIG. 1C to form a sub-island (Post-LC) 13 with enhancedcrystallinity. In the present invention, a portion of a beam spot thatis low in energy density is cut off by a slit 17. The slit 17 isdesirably formed of a material that can block laser light and is notdeformed or damaged by laser light. The width of the slit in the slit 17is variable and a beam spot can be changed in width by changing thewidth of the slit.

A laser beam is judged as being low in energy density when it does notmeet the value necessary to obtain desired crystals. Whether a crystalqualifies as a desired crystal or not is appropriately decided atdesigner's discretion. Therefore, if a laser beam cannot provide thecrystallinity that the designer wants, the laser beam is judged as beinglow in energy density.

The laser light energy density is lower in the vicinity of edges of abeam spot that has passed through the slit. The vicinity of edgestherefore can only provide small crystal grains and causes a ridge alongthe grain boundary. For that reason, edges 15 of the track of a beamspot 14 of laser light has to be prevented from overlapping thesub-island (Pre-LC) 12 or an island formed after the sub-island.

The laser light scanning direction is determined such that, as the beamspot reaches the sub-island during laser light scanning, one point ofthe beam spot comes into contact with the sub-island viewed from thedirection perpendicular to the substrate. Laser light irradiation isstarted from the one contact point to commence growth of crystals having<100> orientation from the vicinity of the contact point. Whenirradiation of the sub-island with laser light is finished, the <100>orientation ratio of the entire sub-island is now improved.

The present invention can employ known lasers. A pulse oscillation orcontinuous wave gas laser or solid-state laser may be employed. Examplesof the gas laser include an excimer laser, an Ar laser, and a Kr laser.Examples of the solid-state laser include a YAG laser, a YVO₄ laser, aYLF laser, a YAlO₃ laser, a glass laser, a ruby laser, an alexandritelaser, a Ti:sapphire laser, and a Y₂O₃ laser. The solid-state laseremployed is a laser that uses crystals of YAG, YVO₄, YLF, YAlO₃ or thelike doped with Cr, Nd, Er, Ho, Ce, Co, Ti, Yb, or Tm. The fundamentalwave of the laser is varied depending on the material used for dopingbut laser light obtained has a fundamental wave of about 1 μm. Anon-linear optical element is used to obtain harmonic of the fundamentalwave.

Ultraviolet laser light may also be employed. The ultraviolet laserlight is obtained by using a non-linear optical element to convertinfrared laser light that is emitted from a solid-state laser into greenlaser light and then using another non-linear optical element to convertthe green laser light.

The marker 19 may not be irradiated with laser light.

Next, the sub-island (Post-LC) 13 is patterned as shown in FIG. 1D toform an island 16. Desirably, a portion at the center of the sub-islandthat has better crystallinity is used to form the island 16 whilediscarding the vicinity of edges of the sub-island. The marker 19 is notremoved by the patterning but is left for mask positioning in a laterstep.

The island 16 formed through the above steps has excellent crystallinityas well as enhanced <100> orientation ratio.

The description given next is about the shape of a beam spot synthesizedby overlapping plural beam spots.

FIG. 4A shows an example of the beam spot shape on a processing objectwhen laser light emitted from plural laser oscillation apparatuses doesnot pass through a slit. The beam spot shown in FIG. 4A has anelliptical shape. In the present invention, the beam spot shape of laserlight emitted from laser oscillation apparatus is not limited to anellipse. The beam spot shape is varied depending on the laser type andmay be shaped by an optical system. For instance, the shape of laserlight emitted from the XeCl excimer laser (wavelength: 308 nm, pulsewidth: 30 ns) L3308, a product of Lambda Physik, is a 10 mm×30 mm (eachis half width in beam profile) rectangle. The shape of laser lightemitted from a YAG laser is circular if the rod is cylindrical and isrectangular if the rod is slab-like. Such laser light may be furthershaped by an optical system to give the laser light a desired size.

FIG. 4B shows the energy density distribution of laser light in thedirection of a major axis Y of the beam spot shown in FIG. 4A. Theenergy density distribution of laser light whose beam spot has anelliptical shape becomes higher toward a center O of the ellipse. αcorresponds to the width in the direction of a major axis Y where theenergy density exceeds the value necessary to obtain desired crystals.

FIG. 2A shows the beam spot shape of when laser light that have the beamspot shown in FIGS. 4A and 4B are synthesized. In the case shown in FIG.2A, one linear beam spot is formed by overlapping four laser beam spots.However, the number of beam spots overlapped is not limited thereto.

As shown in FIG. 2A, the beam spots of the laser beams are synthesizedby lining the ellipses up along their major axes to have them partiallyoverlapped with one another. One beam spot 18 is thus formed.Hereinafter, the straight line obtained by connecting centers O of theellipses will be called a central axis.

FIG. 2B shows the laser light energy density distribution in a centralaxis y of the synthesized beam spot shown in FIG. 2A. The beam spotshown in FIG. 2A corresponds to a region that meets the peak energydensity 1/e² in FIG. 2B. In the portions where the beam spots beforesynthesization overlap one another, the energy density is added. Forinstance, as shown in the drawing, energy densities E1 and E2 of theoverlapping beams are added and the sum is almost equal to the peakenergy density of the beam, E3. The energy density is thus evened outbetween the centers O of the ellipses.

The sum of E1 and E2 is ideally E3 but this is not always true inpractice. The acceptable deviation of the sum of E1 and E2 from E3 canbe set appropriately at designer's discretion.

As FIG. 2B shows, the crystallinity of a semiconductor film can beenhanced more efficiently when plural laser beams are overlapped tocompensate one another's low energy density portions than when using asingle laser beam. Assume that the energy density value necessary toobtain desired crystals is met only in the hatched regions of FIG. 1Band not in the rest as a result of irradiation by a single beam spot. Inthis case, only a hatched region of the beam spot whose width in thecentral axis direction is α can provide desired crystals. If beam spotsare overlapped instead as shown in FIG. 2B, a region whose width in thecentral axis direction is β (β>4α) can provide desired crystals and asemiconductor film can be crystallized more efficiently.

The energy density distributions in B-B′ and C-C′ of FIG. 2A arecalculated and shown in FIGS. 3A and 3B, respectively. In FIGS. 3A and3B, regions of beam spots before synthesization where the peak energydensity 1/e² is met are used as the reference. The energy densitydistributions in B-B′ and C-C′ shown in FIGS. 3A and 3B are of when eachbeam spot before synthesization measures 37 μm in length in the minoraxis direction and 410 μm in length in the major axis direction and thedistance between centers of the beam spots is set to 192 μm. Althoughthe distribution in B-B′ is slightly smaller than the distribution inC-C′, the two have almost the same size. Therefore, it can be said thatthe shape of the synthesized beam spot is linear in the regions of thebeam spots before synthesization where the peak energy density 1/e² ismet.

There are regions where the energy density fails to meet the desiredvalue even after laser beams are overlapped. The present invention usesthe slit 17 to cut off the low energy density regions of the synthesizedbeam spot and prevents them from irradiating the semiconductor film 11.The positional relation between the synthesized beam spot and the slitis described with reference to FIG. 2C.

The slit 17 used in the present invention has a slit variable in widthand the width is controlled by a computer. In FIG. 2C, 18 denotes theshape of the beam spot 18 obtained by synthesization as the one shown inFIGS. 2A and 17 denotes the slit.

FIG. 2D shows the energy density distribution in a direction y that isthe direction of the central axis A-A′ of the beam spot shown in FIG.2B. Unlike the case shown in FIG. 3B, regions low in energy density arecut off by the slit 17.

A semiconductor film irradiated with a region of laser light that is lowin energy density has poor crystallinity. Specifically, crystal grainsof such film are smaller in size than ones in a film irradiated with alaser light region having enough energy density and the crystal grainsgrow in different directions. FIG. 5A shows the shape of a synthesizedbeam spot on a substrate. In a region denoted by 50, a desired energydensity is met. A region denoted by 51 does not meet the desired energydensity. The length in the central axis direction of the beam spot isgiven as W_(TBW), the length in the central axis direction of the regionhaving enough energy density is given as W_(BW), and the length in thedirection perpendicular to the central axis direction of the regionhaving enough energy density is given as W_(C).

FIG. 5B shows the positional relation between the scanning path of abeam spot 52 and a sub-island pattern. The length in the central axisdirection of the beam spot 52 is set equal to or less than W_(BW) bymaking the beam spot shown in FIG. 5A travel through a slit. FIG. 5Bshows scanning by the beam spot 52 whose low energy density portions arecut off widthwise in the direction perpendicular to the scanningdirection. The beam spot 52 runs so as to cover a sub-island 53 andedges of the track of the beam spot does not overlap the sub-island 53.It is not always necessary to prevent the edges of the track of the beamspot from overlapping the sub-island. What is important is to preventthe edges from overlapping an island 54 that is obtained through theminimum patterning of the sub-island.

In the present invention, there is no low energy density region, or ifthere is any, the width thereof is smaller than in the case where a slitis not used. This makes it easier to avoid overlapping of laser lightedges and the sub-island 53. By using a slit, regions low in energydensity are cut off and therefore limitations in setting the laser lightscanning path and layout of a sub-island and island can be reduced.

Also the present invention can prevent laser light edges fromoverlapping an island or its channel formation region because the beamspot width can be changed without stopping output of laser oscillationapparatus while keeping the energy density constant. A portion that doesnot need laser irradiation is not irradiated with laser light andtherefore damage to the substrate can be avoided.

In the case shown in FIGS. 5A and 5B, the central axis direction of thebeam spot is kept perpendicular to the scanning direction. However, itis not always necessary to set the central axis direction of the beamspot perpendicular to the scanning direction. For example, an acuteangle θ_(A) formed between the central axis direction of the beam spotand the scanning direction may be set to 45°±35°, desirably 45°. Thesubstrate processing efficiency is the highest when the central axis ofa beam spot is perpendicular to the scanning direction. On the otherhand, when the central axis of a synthesized beam spot and the scanningdirection form an angle of 45°±35°, desirably closer to 45°, crystalgrains present in the active layer can be increased in number than whenthe central axis of the beam spot is perpendicular to the scanningdirection. Accordingly, fluctuation in characteristic due to crystalorientation and crystal grains can be reduced. In addition, if thescanning speed is the same, the laser light irradiation time persubstrate is longer when the central axis of a synthesized beam spot andthe scanning direction form an angle of 45°±35° than when the centralaxis of the beam spot is perpendicular to the scanning direction.

Next, a description is given on the relation between the shapes of asub-island and island and the laser light scanning direction. FIG. 6A isa top view of the sub-island 12 shown in FIG. 1B. A portion 16 to be anisland is indicated by a dashed line inside the sub-island (Pre-LC) 12.Denoted by 14 is a beam spot, which in FIG. 6A is in a state beforelaser irradiation.

From the state in FIG. 6A, the beam spot 14 approaches the sub-island(Pre-LC) 12 as time passes. The position of the beam spot is changed bymoving the substrate.

As the beam spot 14 reaches the sub-island (Pre-LC) 12, one point of thebeam spot 14 comes into contact with the sub-island (Pre-LC) 12.Crystallization of the sub-island begins from the vicinity of thiscontact point, which is denoted by 20, and the crystallization proceedsin the direction indicated by the arrow as the beam spot 14 moves asshown in FIG. 6C. Since the crystallization starts from a seed crystalformed in the contact point vicinity 20 first, the <110> orientationratio is raised.

When the island is used as an active layer of a TFT, the laser lightscanning direction is desirably kept parallel to the direction in whichcarriers of a channel formation region move.

The track of the beam spot 14 may not completely cover the sub-island12, and it only has to cover the island 16 completely. However, byrunning laser light so as to completely cover the sub-island, a regionthat is not irradiated with laser light is prevented from working as aseed crystal for crystal growth and the <110> orientation ratio can beenhanced more.

FIG. 6D shows a sectional view taken along the line A-A′ of FIG. 6C inrelation to the beam spot. Laser light that has passed through the slit17 to irradiate the substrate is partially blocked by the slit and itswidth W_(TDW) in the major axis direction is reduced to W_(BW). Then,ideally, the beam spot of the laser light on the sub-island becomesequal in width with W_(BW). However, the slit 17 is actually distancedfrom the sub-island 12 and therefore the actual width in the major axisdirection of the beam spot of the laser light is W_(BW)′ on thesub-island 12. W_(BW)′ is smaller than W_(BW). (W_(BW)′<W_(BW)).Therefore, it is desirable to set the slit width taking diffraction intoconsideration.

In irradiating the entire sub-island with laser light, it is sufficientif W_(BW)>W_(S) is satisfied when diffraction is not taken into accountand W_(BW)′>W_(S) is satisfied when diffraction is taken into account.In the minimum laser irradiation for irradiating the island alone, it issufficient if W_(BW)>W_(I) is satisfied when diffraction is not takeninto account and W_(BW)′>W_(I) is satisfied when diffraction is takeninto account. W_(S) is the longest length of the sub-island 12 in thedirection perpendicular to the moving direction of the beam spot. W_(I)represents the longest length of the island 16 in the directionperpendicular to the moving direction of the beam spot.

FIGS. 7A and 7B show examples of layout of an island used as an activelayer of a TFT in relation to the moving direction of a beam spot. InFIG. 7A, a portion 31 indicated by the dashed line inside a sub-island30 becomes an island. When the island 31 is used as an active layer of aTFT which has one channel formation region, impurity regions 33 and 34are provided so as to sandwich a channel formation region 32. One of theimpurity regions 33 and 34 serves as a source region and the otherserves as a drain region. The reference numeral 35 shows the shape ofthe beam spot. In crystallizing the sub-island 30, the laser lightscanning direction is set parallel to the direction in which carriers ofthe channel formation region 32 move as indicated by the arrow. Onepoint of the beam spot 35 is in contact with the sub-island. A seedcrystal is formed in the vicinity of the contact point, which is denotedby 36, and crystals grow from the seed crystal. The <110> orientationratio of the sub-island is thus enhanced.

FIG. 7B shows an active layer having three channel formation regions.Impurity regions 41 and 42 are provided so as to sandwich a channelformation region 40. The impurity region 42 and an impurity region 44are provided so as to sandwich a channel formation region 43. Theimpurity region 44 and an impurity region 46 are provided so as tosandwich a channel formation region 45. The beam spot runs in parallelto the direction in which carriers of the channel formation regions 40,43, and 45 move as indicated by the arrow.

Described next with reference to FIG. 8A is the laser light scanningdirection on a substrate 500 where a sub-island is formed to manufacturean active matrix semiconductor device. In FIG. 8A, a pixel portion, asignal line driving circuit, and a scanning line driving circuit areformed in the areas indicated by dashed lines 501, 502, and 503,respectively.

In the example shown in FIG. 8A, laser light runs over the substrate 500only once. The substrate moves in the direction indicated by theoutlined arrow and the solid line arrow indicates the relative laserlight scanning direction. The beam spot may be moved by moving thesubstrate 500 or by using an optical system. FIG. 8B is an enlarged viewof a beam spot 507 in the area 501 where the pixel portion is to beformed. Sub-islands 506 are laid out in a region irradiated with laserlight.

It is desirable in FIGS. 8A and 8B to irradiate the substrate with laserlight so as to prevent edges of the beam spot from overlapping islands508, more desirably, the sub-islands 506. The islands 508 are obtainedby patterning the sub-islands. In the present invention, which portionis to be scanned with laser light is determined in accordance withpattern information of a mask of a sub-island.

The beam spot width can be changed to suite the size of a sub-island orisland. For example, in a TFT of a driving circuit where a relativelylarge amount of current flows, the channel width is large andaccordingly the island size tends to be larger than in a pixel portion.In FIGS. 9A and 9B, the slit width is changed to run laser light overtwo types of sub-islands having different sizes. FIG. 9A shows therelation between a portion scanned with laser light and a sub-islandwhen the sub-island is shorter in the direction perpendicular to thescanning direction. FIG. 9B shows the relation between a portion scannedwith laser light and a sub-island when the sub-island is longer in thedirection perpendicular to the scanning direction.

When the beam spot width in FIG. 9A is given as W_(BW1) and the beamspot width in FIG. 9B is given as W_(BW2), W_(BW1) is smaller thanW_(BW2). The beam spot width is not limited thereto and can be setfreely if there is a margin in the gap between sub-islands in thedirection perpendicular to the scanning direction.

The present invention runs laser light so as to obtain the minimumdegree of crystallization of a sub-island as shown in FIGS. 9A and 9B,instead of irradiating the entire surface of the substrate with laserlight. Since the minimum portion is irradiated with laser light so thata sub-island is crystallized instead of irradiating the entire surfaceof a substrate, the processing time per substrate can be reduced toraise the substrate processing efficiency.

Next, a description is given with reference to FIG. 10 on the structureof laser irradiation apparatus used in the present invention. Thereference numeral 101 denotes a laser oscillation apparatus. Four laseroscillation apparatuses are used in FIG. 10 but the number of laseroscillation apparatuses in the laser irradiation apparatus is notlimited thereto.

A chiller 102 may be used to keep the temperature of the laseroscillation apparatus 101 constant. Although the chiller 102 is notalways necessary, fluctuation in energy of laser light outputted due toa temperature change can be avoided by keeping the temperature of thelaser oscillation apparatus 101 constant.

Denoted by 104 is an optical system, which changes the path of lightemitted from the laser oscillation apparatus 101 or manipulates theshape of its beam spot to collect laser light. In the laser irradiationapparatus of FIG. 10, the optical system 104 can also synthesize beamspots of laser light outputted from the plural laser oscillationapparatuses 101 by partially overlapping the beam spots.

An AO modulator 103 capable of changing the travel direction of laserlight in a very short time may be provided in the light path between asubstrate 106 that is a processing object and the laser oscillationapparatus 101. Instead of the AO modulator, an attenuator (light amountadjusting filter) may be provided to adjust the energy density of laserlight.

Alternatively, energy density measuring means 115, namely, means formeasuring the energy density of laser light outputted from the laseroscillation apparatus 101 may be provided in the light path between thesubstrate 106 that is a processing object and the laser oscillationapparatus 101. Changes with time of measured energy density aremonitored by a computer 110. In this case, output from the laseroscillation apparatus 101 may be increased to compensate attenuation inenergy density of the laser light.

A synthesized beam spot irradiates through a slit 105 the substrate 106that is a processing object. The slit 105 is desirably formed of amaterial that can block laser light and is not deformed or damaged bylaser light. The width of the slit in the slit 165 is variable and abeam spot can be changed in width by changing the width of the slit.

When laser light emitted from the laser oscillation apparatus does notpass through the slit 105, the shape of its beam spot on the substrate106 is varied depending on the laser type and may be shaped by anoptical system.

The substrate 106 is set on a stage 107. In FIG. 10, positioncontrolling means 108 and 109 correspond to means for controlling theposition of a beam spot on a processing object. The position of thestage 107 is controlled by the position controlling means 108 and 109.

In FIG. 10, the position controlling means 108 controls the position ofthe stage 107 in the direction X and the position controlling means 109controls the position of the stage 107 in the direction Y.

The laser irradiation apparatus of FIG. 10 has the computer 110, whichis a central processing unit and at the same time storing means such asa memory. The computer 110 controls oscillation of the laser oscillationapparatus 101 and controls the position controlling means 108 and 109 tomove the substrate to a given position so that a beam spot of laserlight covers a region determined in accordance with mask patterninformation.

In the present invention, the computer 110 also controls the width ofthe slit 105 so that the beam spot width can be changed in accordancewith mask pattern information.

The laser irradiation apparatus may also has means for adjusting thetemperature of a processing object. A damper may also be provided toprevent reflected light from irradiating a portion that should avoidlaser irradiation since laser light is highly directional and has highenergy density. Desirably, the damper is absorptive of reflected light.Cooling water may be circulated inside the damper to avoid a temperaturerise of the partition wall due to absorption of reflected light. Thestage 107 may be provided with means for heating a substrate (substrateheating means).

If a laser is used to form a marker, laser oscillation apparatus for amarker may be provided. In this case, oscillation of the laseroscillation apparatus for a marker may be controlled by the computer110. Another optical system is needed when the laser oscillationapparatus for a marker is provided in order to collect laser lightoutputted from the laser oscillation apparatus for a marker. The laserused to form a marker is typically a YAG laser or a CO₂ laser but otherlasers may be employed.

One or more CCD cameras 113 may be provided for positioning using amarker.

Instead of forming a marker, the CCD camera(s) 113 may be used torecognize the pattern of a sub-island for positioning. In this case,sub-island pattern information by a mask which is inputted to thecomputer 110 and the actual sub-island pattern information collected bythe CCD camera(s) 113 are checked against each other to obtain thesubstrate position information.

Although FIG. 10 shows a structure of a laser irradiation apparatuswhich has plural laser oscillation apparatuses, only one laseroscillation apparatus may be provided. FIG. 11 shows a laser irradiationapparatus structure which has one laser oscillation apparatus. In FIG.11, 201 denotes a laser oscillation apparatus and 202 denotes a chiller.Denoted by 215 is an energy density measuring device, 203, an AOmodulator, 204, an optical system, 205, a slit, and 213, a CCD camera. Asubstrate 206 is set on a stage 207. The position of the stage 207 iscontrolled by X-direction position controlling means 208 and Y-directionposition controlling means 209. Similar to the apparatus shown in FIG.10, a computer 210 controls operations of the respective means of thislaser irradiation apparatus. The major difference between FIG. 11 andFIG. 10 is that there is one laser oscillation apparatus in FIG. 11.Unlike FIG. 10, the optical system 204 only has to have a function ofcollecting one laser beam.

Next, the flow of a semiconductor device manufacturing method of thepresent invention will be described.

FIG. 12 is a flow chart showing production flow. First, a semiconductordevice is designed using CAD. Specifically, a mask for an island isdesigned first and then a mask for a sub-island that includes one ormore of such islands is designed. In designing the masks, all islandsincluded in one sub-island are desirably arranged such that the carriersof their channel formation regions move in the same direction. However,the moving direction may be varied intentionally if doing so suits theuse of the semiconductor device.

The mask for a sub-island may be designed such that a marker is formedat the same time the sub-island is formed.

Then, information concerning the shape of the designed mask for asub-island (pattern information) is inputted to a computer of laserirradiation apparatus. From the sub-island pattern information inputted,the computer calculates a width W_(S) of each sub-island in thedirection perpendicular to the scanning direction. Based on the widthW_(S) of each sub-island, a slit width W_(BW) in the directionperpendicular to the scanning direction is set.

Then, the laser light scanning path is determined based on the slitwidth W_(BW) with the marker position as the reference.

During this, a semiconductor film is formed on a substrate and thesemiconductor film is patterned using the mask for a sub-island to forma sub-island. The substrate on which the sub-island is formed is set ona stage of the laser irradiation apparatus.

With the marker as the reference, laser light runs along the setscanning path targeting the sub-island to crystallize the sub-island.

The sub-island having its crystallinity enhanced by the laser lightirradiation is patterned to form an island. Subsequently, a process ofmanufacturing a TFT from the island follows. Although specifics of theTFT manufacturing process are varied depending on the TFT form, atypical process starts with forming a gate insulating film and formingan impurity region in the island. Then, an interlayer insulating film isformed so as to cover the gate insulating film and a gate electrode. Acontact hole is formed in the interlayer insulating film to partiallyexpose the impurity region. A wiring is then formed on the interlayerinsulating film to reach the impurity region through the contact hole.

Described next is an example of positioning a substrate and a mask by aCCD camera without forming a marker.

FIG. 13 is a flow chart showing production flow. First, similar to thecase of FIG. 12, a semiconductor device is designed using CAD.Specifically, a mask for an island is designed first and then a mask fora sub-island that includes one or more of such islands is designed.

Then, information concerning the shape of the designed mask for asub-island (pattern information) is inputted to a computer of laserirradiation apparatus. From the sub-island pattern information inputted,the computer calculates a width W_(S) of each sub-island in thedirection perpendicular to the scanning direction. Based on the widthW_(S) of each sub-island, a slit width W_(BW) in the directionperpendicular to the scanning direction is set.

During this, a semiconductor film is formed on a substrate and thesemiconductor film is patterned using the mask for a sub-island to forma sub-island. The substrate on which the sub-island is formed is set ona stage of the laser irradiation apparatus.

Then, pattern information of the sub-island formed on the substrate thatis set on the stage is detected by the CCD camera and inputted to thecomputer. The computer checks the pattern information of the sub-islandactually formed on the substrate which is obtained by the CCD cameraagainst the pattern information of the sub-island designed by the CADfor positioning of the substrate and the mask.

The laser light scanning path is determined based on the slit widthW_(BW) and the sub-island position information provided by the CCDcamera.

Then, laser light runs along the set scanning path targeting thesub-island to crystallize the sub-island.

The sub-island having its crystallinity enhanced by the laser lightirradiation is patterned to form an island. Subsequently, a process ofmanufacturing a TFT from the island follows. Although specifics of theTFT manufacturing process are varied depending on the TFT form, atypical process starts with forming a gate insulating film and formingan impurity region in the island. Then, an interlayer insulating film isformed so as to cover the gate insulating film and a gate electrode. Acontact hole is formed in the interlayer insulating film to partiallyexpose the impurity region. A wiring is then formed on the interlayerinsulating film to reach the impurity region through the contact hole.

FIG. 14 is a flow chart showing the flow of a producing method in whicha processing object is irradiated with laser light twice.

First, a semiconductor device is designed using CAD. Specifically, amask for an island is designed first and then a mask for a sub-islandthat includes one or more of such islands is designed. The mask for asub-island may be designed such that a marker is formed at the same timethe sub-island is formed.

Then, information concerning the shape of the designed mask for asub-island (pattern information) is inputted to a computer of laserirradiation apparatus. From the sub-island pattern information inputted,the computer calculates for each sub-island two widths W_(S) in thedirections perpendicular to two scanning directions. Slit widths W_(BW)in the directions perpendicular to the two scanning directions arecalculated based on the widths W_(S) of each sub-island.

Then, the laser light scanning path in each of the two scanningdirections is determined based on the respective slit widths W_(BW) withthe marker position as the reference.

During this, a semiconductor film is formed on a substrate and thesemiconductor film is patterned using the mask for a sub-island to forma sub-island. The substrate on which the sub-island is formed is set ona stage of the laser irradiation apparatus.

With the marker as the reference, a first laser light runs along a firstscanning path, namely, one of the two scanning paths set, targeting thesub-island to crystallize the sub-island.

The angle the first time laser light scanning direction and the secondtime laser light scanning direction form may be stored in advance in amemory or the like, or may be inputted manually as the need arises.

The scanning direction is then changed and the second laser light runsalong the second scanning path targeting the sub-island to crystallizethe sub-island.

In the example shown in FIG. 14, the same sub-island is twice irradiatedwith laser light. However, it is also possible to change the scanningdirection specifying the location if an AO modulator or the like isemployed. For instance, when the scanning direction in a signal linedriving circuit is different from the scanning direction in a pixelportion and a scanning line driving circuit and an AO modulator is usedto irradiate with laser light an area to become the signal line drivingcircuit, the AO modulator prevents laser light from irradiating areas tobecome the pixel portion and the scanning line driving circuit. Ifinstead the areas to become the pixel portion and the scanning linedriving circuit are irradiated with laser light, the AO modulatorprevents laser light from irradiating the area to become the signal linedriving circuit. In this case, the computer synchronizes the AOmodulator with the position controlling means.

The sub-island having its crystallinity enhanced by the laser lightirradiation is patterned to form an island. Subsequently, a process ofmanufacturing a TFT from the island follows. Although specifics of theTFT manufacturing process are varied depending on the TFT form, atypical process starts with forming a gate insulating film and formingan impurity region in the island. Then, an interlayer insulating film isformed so as to cover the gate insulating film and a gate electrode. Acontact hole is formed in the interlayer insulating film to partiallyexpose the impurity region. A wiring is then formed on the interlayerinsulating film to reach the impurity region through the contact hole.

For comparison, the flow of a conventional semiconductor deviceproducing method is shown in FIG. 15. As shown in FIG. 15, a mask of asemiconductor device is designed using CAD. An amorphous semiconductorfilm is formed on a substrate, and the substrate on which the amorphoussemiconductor film is formed is set in laser irradiation apparatus.Then, laser light runs over the substrate so that the entire amorphoussemiconductor film is irradiated with laser light. As a result, theentire amorphous semiconductor film is crystallized. A marker is formedin the polycrystalline semiconductor film obtained by thecrystallization, and the polycrystalline semiconductor film is patternedwith the marker as the reference to form an island. Then, a TFT isformed from the island.

As described, unlike prior art as the one shown in FIG. 15, the presentinvention uses laser light to form a marker before an amorphoussemiconductor film is crystallized. The present invention then runslaser light in accordance with information of a mask for patterning ofthe semiconductor film.

With the above structure, time for laser irradiation of portions thatare removed by patterning after crystallization of the semiconductorfilm can be saved to shorten the whole laser irradiation time andimprove the substrate processing speed.

A step of crystallizing a semiconductor film using a catalyst may beincluded. If a catalytic element is used, it is desirable to employtechniques disclosed in JP 07-130652 A and JP 08-78329 A.

When a step of crystallizing a semiconductor film using a catalyst isincluded, the process includes a step of crystallizing an amorphoussemiconductor film by using Ni after the film is formed (NiSPC). Forexample, if the technique disclosed in JP 07-130652 A is used, a nickelacetate solution containing 10 ppm of nickel by weight is applied to anamorphous semiconductor film to form a nickel-containing layer. After adehydrogenation step at 500° C. for an hour, the amorphous semiconductorfilm is subjected to heat treatment at 500 to 650° C. for 4 to 12 hours,for example, at 550° C. for 8 hours, for crystallization. Examples ofother employable catalytic elements than nickel (Ni) include germanium(Ge), iron (Fe), palladium (Pd), tin (Sn), lead (Pb), cobalt (Co),platinum (Pt), copper (Cu), and gold (Au).

The crystallinity of the semiconductor film that has been crystallizedthrough NiSPC is further enhanced by laser light irradiation. Thepolycrystalline semiconductor film obtained by the laser lightirradiation contains the catalytic element, which is removed from thecrystalline semiconductor film by gettering after the laser lightirradiation. For gettering, a technique disclosed in JP 10-135468 A orJP 10-135469 A can be employed.

To be specific, a part of the polycrystalline semiconductor filmobtained through the laser irradiation is doped with phosphorus and thensubjected to heat treatment at 550 to 800° C. for 5 to 24 hours, forexample, at 600° C. for 12 hours in a nitrogen atmosphere. This causesthe phosphorus-doped region of the polycrystalline semiconductor film toact as a gettering site, so that nickel present in the polycrystallinesemiconductor film is moved to the phosphorus-doped region andsegregated. After that, the phosphorus-doped region of thepolycrystalline semiconductor film is removed by patterning to obtain anisland in which the catalytic element concentration is reduced down to1×10¹⁷ atoms/cm³ or less, preferably, 1×10¹⁶ atoms/cm³ or less.

Next, a description is given with reference to FIGS. 16A and 16B on thepositional relation between a slit and a beam spot when the central axisof the beam spot is kept at 45° with respect to the scanning direction.Denoted by 130 is a beam spot after synthesization and 105 denotes aslit. The slit 105 does not overlap the beam spot 130. The arrowindicates the scanning direction, which forms an angle θ with thecentral axis of the beam spot 130. The angle θ is kept to 45°.

FIG. 16B shows a beam spot 131 obtained by partially blocking laserlight with the slit 105 to reduce the width. In the present, invention,the slit 105 controls a width Q of a beam spot in the directionperpendicular to the scanning direction for uniform laser lightirradiation.

As described, the present invention runs laser light so as to obtain atleast the minimum degree of crystallization of a portion that has to becrystallized, instead of irradiating the entire semiconductor film withlaser light. With the above structure, time for laser irradiation ofportions that are removed by patterning after crystallization of thesemiconductor film can be saved to greatly shorten the laser irradiationtime per substrate.

Embodiments of the present invention will be described below.

Embodiment 1

This embodiment describes optical systems of laser irradiation apparatusused in the present invention, and the positional relation between aslit and each of the optical systems.

FIGS. 17A to 17D show optical systems of this embodiment. The opticalsystem shown in FIG. 17A has two cylindrical lenses 401 and 402. Laserlight entering from the direction indicated by the arrow passes throughthe two cylindrical lenses 401 and 402, which modify the shape of thebeam spot of the laser light. The beam spot travels through a slit 404to irradiate a processing object 403. Of the cylindrical lenses 401 and402, 402 is closer to the processing object 403 and has a shorter focallength. In order to avoid return light and irradiate uniformly, theincident angle at which laser light enters the substrate is set tolarger than 0°, desirably, 5 to 30°.

The optical system shown in FIG. 17B has a mirror 405 and a planoconvexspherical lens 406. Laser light entering from the direction indicated bythe arrow is reflected by the mirror 405, and the shape of the beam spotof the laser light is modified by the planoconvex spherical lens 406.The beam spot travels through a slit 408 to irradiate a processingobject 407. The radius of curvature of the planoconvex spherical lenscan be set appropriately at designer's discretion. In order to avoidreturn light and irradiate uniformly, the incident angle at which laserlight enters the substrate is set to larger than 0°, desirably, 5 to30°.

The optical system shown in FIG. 17C has mirrors 410 and 411 and lenses412, 413, and 414. Laser light entering from the direction indicated bythe arrow is reflected by the mirrors 410 and 411, and the shape of thebeam spot of the laser light is modified by the lenses 412, 413, and414. The beam spot travels through a slit 416 to irradiate a processingobject 415. In order to avoid return light and irradiate uniformly, theincident angle at which laser light enters the substrate is set tolarger than 0°, desirably, 5 to 30°.

FIG. 17D shows an optical system for synthesizing four beam spots shownin Embodiment 2 to obtain one beam spot. The optical system shown inFIG. 17D has six cylindrical lenses 417 to 422. Four laser beamsentering the optical system from the directions indicated by the arrowsenter the four cylindrical lenses 419 to 422, respectively. Two laserbeams shaped by the cylindrical lenses 419 and 421 reach the cylindricallens 417, which modifies the shapes of their beam spots. The beam spotstravel through a slit 424 to irradiate a processing object 423. On theother hand, two laser beams shaped by the cylindrical lenses 420 and 422reach the cylindrical lens 418, which modifies the shapes of their beamspots. The beam spots travel through the slit 424 to irradiate theprocessing object 423.

The beam spots of the laser beams on the processing object 423 partiallyoverlap one another for synthesization, thereby forming one beam spot.

The focal length and incident angle of each lens can be setappropriately at designer's discretion. However, the focal length of thecylindrical lenses 417 and 418 which are the closest to the processingobject 423 is set shorter than the focal length of the cylindricallenses 419 to 422. For example, the focal length of the cylindricallenses 417 and 418 which are the closest to the processing object 423 isset to 20 mm whereas the focal length of the cylindrical lenses 419 to422 is set to 150 mm. In this embodiment, the lenses are arranged suchthat laser beams enter the processing object 423 from the cylindricallenses 417 and 418 at an incident angle of 25° and laser beams enter thecylindrical lenses 417 and 418 from the cylindrical lenses 419 to 422 atan incident angle of 10°. In order to avoid return light and irradiateuniformly, the incident angle at which laser light enters the substrateis set to larger than 0°, desirably, 5 to 30°.

In the example shown in FIG. 17D, four beam spots are synthesized. Inthis case, four cylindrical lenses respectively associated with fourlaser oscillation apparatuses and two cylindrical lenses associated withthe four cylindrical lenses are provided. The number of beam spotssynthesized is not limited to 4. It is sufficient if the number of beamspots synthesized is equal to or more than 2 and equal to or less than8. When n (n=2, 4, 6, 8) beam spots are synthesized, n cylindricallenses respectively associated with n laser oscillation apparatuses andn/2 cylindrical lenses associated with the n cylindrical lenses areprovided. When n (n=3, 5, 7) beam spots are synthesized, n cylindricallenses respectively associated with n laser oscillation apparatuses and(n+1)/2 cylindrical lenses associated with the n cylindrical lenses areprovided.

When five or more beam spots are synthesized, the fifth and thefollowing laser beams desirably irradiate a substrate from the oppositeside of the substrate, taking into consideration where to place theoptical system, interference, and the like. In this case, another slitis needed on the opposite side of the substrate. Also, the substrate hasto be transmissive.

In order to prevent light from traveling back its light path (returnlight), the incident angle at which laser light enters the substrate isdesirably kept at larger than 0° and smaller than 90°.

A plane which is perpendicular to the irradiated face and which includesa shorter side of the rectangular shape of each beam beforesynthesization, or a longer side thereof, is defined as an incidentplane. When the length of the shorter side or longer side included inthe incident plane is given as W, and the thickness of a substrate whichis transmissive of the laser light and which is set on the irradiatedface is given as d, an incident angle θ of the laser light desirablysatisfies θ≧arc tan (W/2d) to achieve uniform laser light irradiation.This has to be true in each laser light before synthesization. If thetrack of this laser light is not on the incident plane, the incidentangle of the track projected onto the incident plane is deemed as θ.When laser light enters the substrate at this incident angle θ,interference between light reflected at the front side of the substrateand reflected light from the back side of the substrate can be avoidedto give the substrate uniform laser beam irradiation. The premise of theabove discussion is that the refractive index of the substrate is 1. Inpractice, the refractive index of the substrate is often around 1.5, andthe angle calculated taken this fact into account is larger than theangle calculated in the above discussion. However, the energy of a beamspot is attenuated at its ends in the longitudinal direction andinfluence of interference is small in these portions. Therefore enoughinterference attenuation effect can be obtained with the valuecalculated in the above discussion.

An optical system of the laser irradiation apparatus used in the presentinvention can have other structures than those shown in this embodiment.

Embodiment 2

This embodiment describes an example in which plural laser oscillationapparatuses are used and the width of a beam spot of laser light ischanged by an AO modulator in the middle of laser light irradiation.

In this embodiment, a computer grasps a laser light scanning path basedon mask information inputted. Furthermore, this embodiment uses an AOmodulator to change the direction of laser light outputted from any oneof the plural laser oscillation apparatuses to prevent the redirectedlaser light from irradiating a processing object and thereby change thewidth of the beam spot in accordance with the mask shape. In this case,although the width of the beam spot is changed by the AO modulator, aregion of the beam spot that is low in energy density still has to beblocked in the direction perpendicular to the scanning direction.Therefore, control of the slit width and blocking of laser light by theAO modulator have to be synchronized.

FIG. 18A shows an example of the relation between the shape of a maskfor patterning a semiconductor film and the beam spot width when aprocessing object is irradiated with laser light once. Indicated by 560is the shape of a mask for patterning a semiconductor film. Asemiconductor film is patterned in accordance with the mask after thesemiconductor film is crystallized by laser irradiation.

Denoted by 561 and 562 are areas irradiated with laser light. The areas561 and 562 are scanned with a beam spot obtained by overlapping andsynthesizing laser beams outputted from four laser oscillationapparatuses. A slit controls the beam spot width such that it isnarrower in 562 than in 561.

By using an AO modulator as in this embodiment, the beam spot width canbe changed freely without stopping output of every laser oscillationapparatus and unstable output due to interruption of output of laseroscillation apparatus can be avoided.

With the above structure, the laser light track can be changed in widthand edges of the laser light track can be prevented from overlapping asemiconductor that is obtained by patterning. Also, the above structurefurther reduces damage to a substrate which is caused by irradiatingwith laser light an area that does not need irradiation.

Next, a description is given on an example of blocking laser light by anAO modulator in the middle of laser light irradiation to irradiate onlya given area with laser light. In this embodiment, laser light isblocked by using an AO modulator to change the direction of the laserlight. However, the present invention is not limited thereto and canemploy any measure that can block laser light.

In the present invention, a computer grasps which part is to be scannedwith laser light from mask information inputted. Furthermore, thisembodiment uses an AO modulator to change the direction of laser lightso that the laser light is blocked and an area to be scanned alone isirradiated with laser light. The AO modulator is desirably formed of amaterial which can block laser light and which is not deformed ordamaged by laser light.

FIG. 18B shows an example of the relation between the shape of a maskfor patterning a semiconductor film and an area to be irradiated withlaser light. Indicated by 570 is the shape of a mask for patterning asemiconductor film. A semiconductor film is patterned in accordance withthe mask after the semiconductor film is crystallized by laserirradiation.

Denoted by 571 is an area irradiated with laser light. An areasurrounded by the dashed line is not irradiated with laser light becausean AO modulator changes the direction of laser light to block the laserlight. In this embodiment, an area where crystallization is unnecessaryis not irradiated with laser light, or even if irradiated, laser lightused is low in energy density. Therefore, damage to a substrate which iscaused by irradiating an area that does not need irradiation with laserlight can be further reduced.

Next, a description is given on a process of manufacturing asemiconductor device having a pixel portion, a signal line drivingcircuit, and a scanning line driving circuit, in which an AO modulatoris used for selective laser light irradiation of the pixel portion, thesignal line driving circuit, and the scanning line driving circuit toirradiate each of them once.

First, as shown in FIG. 19A, laser light runs over a signal line drivingcircuit 302 and a pixel portion 301 in the direction indicated by thearrow for laser light irradiation. At this point, instead of irradiatingthe entire surface of the substrate with laser light, an AO modulator isused to change the direction of laser light and block the laser light sothat a scanning line driving circuit 303 is not irradiated with laserlight.

Then, as shown in FIG. 19B, the scanning line driving circuit 303 isirradiated with laser light by running laser light over the scanningline driving circuit 303 in the direction indicated by the arrow. Atthis time, the signal line driving circuit 302 and the pixel portion 301are not irradiated with laser light.

The description given next is about another example of using an AOmodulator for selective laser light irradiation of a pixel portion, asignal line driving circuit, and a scanning line driving circuit toirradiate each of them once.

First, as shown in FIG. 19C, laser light runs over the scanning linedriving circuit 303 and a pixel portion 301 in the direction indicatedby the arrow for laser light irradiation. At this point, instead ofirradiating the entire surface of the substrate with laser light, an AOmodulator is used to change the direction of laser light and block thelaser light so that the signal line driving circuit 302 is notirradiated with laser light.

Then, as shown in FIG. 19D, the signal line driving circuit 302 isirradiated with laser light by running laser light over the signal linedriving circuit 302 in the direction indicated by the arrow. Duringthis, the scanning line driving circuit 303 and the pixel portion 301are not irradiated with laser light.

As described above, using an AO modulator makes selective laserirradiation possible and therefore the laser light scanning directioncan be changed for each circuit in accordance with layout of channelformation regions in active layers of the respective circuits. Sinceirradiating the same circuit with laser light twice can be avoided, iteliminates limitations in laser light path setting and active layerlayout which are for preventing edges of second time laser light fromoverlapping active layers laid out.

Next, an example is described in which plural panels are manufacturedfrom a large-sized substrate when an AO modulator is used for selectivelaser light irradiation of a pixel portion, a signal line drivingcircuit, and a scanning line driving circuit to irradiate each of themonce.

First, as shown in FIG. 20, laser light runs over a signal line drivingcircuit 382 and pixel portion 381 of each panel in the directionindicated by the arrow for laser light irradiation. At this point,instead of irradiating the entire surface of the substrate with laserlight, an AO modulator is used to change the direction of laser lightand block the laser light so that a scanning line driving circuit 383 isnot irradiated with laser light.

Then, the scanning line driving circuit 383 of each panel is irradiatedwith laser light by running laser light over the scanning line drivingcircuit 383 in the direction indicated by the arrow. At this time, thesignal line driving circuit 382 and the pixel portion 381 are notirradiated with laser light. Denoted by 385 is a scrub line of asubstrate 386.

This embodiment can be combined with Embodiment 1.

Embodiment 3

This embodiment describes, in relation to the energy density, thedistance between centers of beam spots when they are overlapped.

In FIG. 21, the energy density distribution in the central axisdirection of each beam spot is indicated by the solid line and theenergy density distribution of the synthesized beam spot is indicated bythe dashed line. The energy density value in the central axis directionof a beam spot generally follows Gaussian distribution.

Assume that, before synthesization, the distance in the central axisdirection of a beam spot where the energy density is equal to or morethan the peak value, 1/e², is 1. Then, the distance between peaks isgiven as X. An increase from the peak value of the average valley valueto the peak value after synthesization is given as Y. The relationbetween X and Y obtained through simulation is shown in FIG. 38. Y inFIG. 38 is expressed as a percentage.

In FIG. 38, the energy difference Y is expressed by the followingExpression 1, which is an approximate expression.Y=60−293X+340X ² (X is the larger one of two solutions.)  [Expression 1]

According to Expression 1, if energy difference is desired to be, forexample, around 5%, X≅0.584 has to be satisfied. Ideally, Y=0 but thismakes the length of the beam spot short. Therefore, X is preferablydetermined balancing it with throughput.

The acceptable range of Y is described next. FIG. 39 shows the output(W) distribution of a YVO₄ laser in relation to the beam width in thecentral axis direction when a beam spot has an elliptical shape. Ahatched region is the range of an energy output necessary to obtainsatisfactory crystallinity. The graph shows that it is sufficient if theoutput energy of synthesized laser light falls between 3.5 W and 6 W.

The energy difference Y for obtaining satisfactory crystallinity reachesits maximum when the maximum value and minimum value of the outputenergy of the synthesized beam spot fall within the range of an energyoutput necessary to obtain satisfactory crystallinity such that thevalues closely match the upper limit and lower limit of the range,respectively. Therefore, in the case of FIG. 39, satisfactorycrystallinity is obtained if the energy difference Y is ±26.3%.

The range of an energy output necessary to obtain satisfactorycrystallinity is varied depending on which level of crystallinity isdeemed as satisfactory, and the output energy distribution is alsovaried depending on the beam spot shape. Accordingly, the acceptablerange of the energy difference Y is not limited to the values describedabove. It is necessary for a designer to determine the range of anenergy output necessary to obtain satisfactory crystallinity and to setthe acceptable range of the energy difference Y from the output energydistribution of the laser light used.

This embodiment can be combined with Embodiment 1 or 2.

Embodiment 4

This embodiment describes how beam spots are overlapped. FIGS. 22A to22C show beam spots before synthesization and their regions where theenergy density is the peak energy density multiplied by 1/e².

FIG. 22A shows a case in which four beam spots are overlapped whileavoiding overlap of the center of one beam spot and the center ofanother beam spot.

FIG. 22B shows a case in which four beam spots are overlapped with thecenter of one beam spot overlapping an edge of another beam spot.

FIG. 22C shows a case of overlapping four beam spots such that thecenter of one beam spot overlaps an edge of a beam spot next to a beamspot that is adjacent to the one beam spot.

The present invention is not limited to these structures. How beam spotsare overlapped can be determined at designer's discretion. Thisembodiment can be combined with Embodiments 1 through 3.

Embodiment 5

This embodiment gives a description with reference to FIGS. 23A to 26 ona method of manufacturing an active matrix substrate using a lasercrystallization method of the present invention. In this specification,a substrate on which a CMOS circuit, a driving circuit, and a pixelportion that has a pixel TFT and capacitor storage are all formed iscalled an active matrix substrate for conveniences' sake.

This embodiment uses glass such as barium borosilicate glass oraluminoborosilicate glass to form a substrate 600. Instead of glass, thesubstrate 600 may be a quartz substrate, silicon substrate, metalsubstrate, or stainless steel substrate with an insulating film formedon its surface. A plastic substrate may also be employed if it hasenough heat resistance to withstand the processing temperature.

On the substrate 600, an insulating film such as a silicon oxide film, asilicon nitride film, or a silicon oxynitride film is formed as a basefilm 601 by a known method (sputtering, LPCVD, plasma CVD, or the like).The base film 601 in this embodiment consists of two layers, base films601 a and 601 b. However, the base film 601 may be a single layer orthree or more layers of the insulating films listed in the above (FIG.23A).

Next, an amorphous semiconductor film 692 is formed on the base film 601by a known method (sputtering, LPCVD, plasma CVD, or the like) to athickness of 25 to 80 nm (preferably 30 to 60 nm) (FIG. 23B). Althoughan amorphous semiconductor film is formed in this embodiment, amicrocrystalline semiconductor film or a crystalline semiconductor filmmay be formed instead. A compound semiconductor film having an amorphousstructure, such as an amorphous silicon germanium film, may also beemployed.

Next, the amorphous semiconductor film 692 is patterned and etched byanisotropic dry etching in an atmosphere containing halogen fluoride,for example, ClF, ClF₃, BrF, BrF₃, IF, or IF₃, to form sub-islands 693a, 693 b, and 693 c.

The sub-islands 693 a, 693 b, and 693 c are crystallized by lasercrystallization. This laser crystallization employs a laser irradiationmethod of the present invention. Specifically, the sub-islands 693 a,693 b, and 693 c are selectively irradiated with laser light inaccordance with mask information inputted to a computer of laserirradiation apparatus. Instead of crystallizing the sub-islands by lasercrystallization alone, other known crystallization methods (such as RTA,thermal crystallization using an annealing furnace, or thermalcrystallization using a metal element that promotes crystallization) maybe used in combination with laser crystallization.

If the amorphous semiconductor film is crystallized by a continuous wavesolid state laser using the second to fourth harmonic of the fundamentalwave thereof, crystals of large grain size can be obtained. Typically,the second harmonic (532 nm) or third harmonic (355 nm) of a Nd:YVO₄laser (fundamental wave: 1064 nm) is desirably employed. To be specific,laser light emitted from a continuous wave YVO₄ laser is converted intoharmonic by a non-linear optical element to obtain laser light withoutput of 10 W. Alternatively, harmonic is obtained by putting a YVO₄crystal and a non-linear optical element in a resonator. The harmonic ispreferably shaped into oblong or elliptical laser light on anirradiation surface by an optical system and then irradiates aprocessing object. The energy density required at this point is around0.01 to 100 MW/cm² (preferably 0.1 to 10 MW/cm²). During theirradiation, the semiconductor film is moved relative to the laser lightat a rate of about 10 to 2000 cm/s.

For laser irradiation, a pulse oscillation or continuous wave gas laseror solid-state laser can be employed. Examples of the gas laser includean excimer laser, an Ar laser, and a Kr laser. Examples of thesolid-state laser include a YAG laser, a YVO₄ laser, a YLF laser, aYAlO₃ laser, a glass laser, a ruby laser, an alexandrite laser, aTi:sapphire laser, and a Y₂O₃ laser. The solid-state laser employed maybe a laser that uses crystals of YAG, YVO₄, YLF, YAlO₃ or the like dopedwith Cr, Nd, Er, Ho, Ce, Co, Ti, Yb, or Tm. The fundamental wave of thelaser is varied depending on the material used for doping but laserlight obtained has a fundamental wave of about 1 μm. A non-linearoptical element is used to obtain harmonic of the fundamental wave.

Through the above laser crystallization, the sub-islands 693 a, 693 b,and 693 c are irradiated with laser light and sub-islands 694 a, 694 b,and 694 c with improved crystallinity are formed (FIG. 23B).

The sub-islands 694 a, 694 b, and 694 c with improved crystallinity arepatterned into desired shapes to form crystallized islands 602 to 606(FIG. 23C).

After the islands 602 to 606 are formed, the islands may be doped with aminute amount of impurity element (boron or phosphorus) in order tocontrol the threshold of TFTs.

Then a gate insulating film 607 is formed to cover the islands 602 to606. The gate insulating film is an insulating film containing siliconand is formed by plasma CVD or sputtering to a thickness of 40 to 150nm. In this embodiment, a silicon oxynitride film (composition ratio:Si=32%, O=59%, N=7%, H=2%) is formed by plasma CVD to a thickness of 110nm. The gate insulating film is not limited to the silicon oxynitridefilm, and a single layer or laminate of other insulating filmscontaining silicon may also be employed.

If a silicon oxide film is chosen for the gate insulating film, it isformed by plasma CVD in which TEOS (tetraethyl orthosilicate) and O₂ aremixed, the reaction pressure is set to 40 Pa, the substrate temperatureto 300 to 400° C., and the high frequency (13.56 MHz) power density to0.5 to 0.8 W/cm² for electric discharge. The thus formed silicon oxidefilm can provide excellent characteristics as a gate insulating film ifit subsequently receives thermal annealing at 400 to 500° C.

Next, a laminate of a first conductive film 608 with a thickness of 20to 100 nm and a second conductive film 609 with a thickness of 100 to400 nm is formed on the gate insulating film 607. In this embodiment, aTaN film with a thickness of 30 nm is formed as the first conductivefilm 608 and then a W film with a thickness of 370 nm is laid thereon asthe second conductive film 609. The TaN film is formed by sputteringwith Ta as the target in an atmosphere containing nitrogen. The W filmis formed by sputtering using a W target. The W film may instead beformed by thermal CVD using tungsten hexafluoride (WF₆). In either case,the W film has to have low resistivity in order to use it as a gateelectrode. Desirably, the W film has a resistivity of 20 μΩcm or less.The resistivity of the W film can be lowered by increasing the grainsize. However, if too many impurity elements such as oxygen arecontained in the W film, crystallization is hindered to raise theresistivity. Accordingly, this embodiment uses sputtering with W of highpurity (purity: 99.9999%) as the target to form the W film taking carenot to allow impurities from the air to mix in the film during itsformation. As a result, the W film can have a resistivity of 9 to 20μΩcm.

Although the first conductive film 608 and the second conductive film609 in this embodiment are a TaN film and a W film, respectively, thereis no particular limitation thereto. The first conductive film andsecond conductive film each can be formed from an element selected fromthe group consisting of Ta, W, Ti, Mo, Al, Cu, Cr, and Nd, or an alloyor compound mainly containing the above elements. Alternatively, thefirst conductive film and the second conductive film may besemiconductor films, typically polycrystalline silicon films, doped withphosphorus or other impurity elements or may be Ag—Pd—Cu alloy films.The following combinations are also employable: a combination of atantalum (Ta) film as the first conductive film and a W film as thesecond conductive film, a combination of a titanium nitride (TiN) filmas the first conductive film and a W film as the second conductive film,a combination of a tantalum nitride (TaN) film as the first conductivefilm and a W film as the second conductive film, a combination of atantalum nitride (TaN) film as the first conductive film and an Al filmas the second conductive film, and a combination of a tantalum nitride(TaN) film as the first conductive film and a Cu film as the secondconductive film.

The present invention is not limited to a two-layer structure conductivefilm. For example, a three-layer structure consisting of a tungstenfilm, aluminum-silicon alloy (Al—Si) film, and titanium nitride filmlayered in this order may be employed. When the three-layer structure isemployed, the tungsten film may be replaced by a tungsten nitride film,the aluminum-silicon alloy (Al—Si) film may be replaced by analuminum-titanium alloy (Al—Ti) film, and the titanium nitride film maybe replaced by a titanium film.

It is important to select the optimum etching method and etchant for theconductive film material employed.

Next, resist masks 610 to 615 are formed by photolithography and thefirst etching treatment is conducted in order to form electrodes andwirings. The first etching treatment employs first and second etchingconditions (FIG. 24B). In this embodiment, the first etching conditionsinclude employing ICP (inductively coupled plasma) etching, using CF₄,Cl₂, and O₂ as etching gas, setting the gas flow rate ratio thereof to25:25:10 (sccm), and applying an RF (13.56 MHz) power of 500 W to acoiled electrode at a pressure of 1 Pa to generate plasma for etching.The substrate side (sample stage) also receives an RF (13.56 MHz) powerof 150 W to apply a substantially negative self-bias voltage. The W filmis etched under these first etching conditions to taper the firstconductive layer around the edges.

Thereafter, the first etching conditions are switched to the secondetching conditions without removing the resist masks 605 to 615. Thesecond etching conditions include using CF₄ and Cl₂ as etching gas,setting the gas flow rate ratio thereof to 30:30 (sccm), and giving anRF (13.56 MHz) power of 500 W to a coiled electrode at a pressure of 1Pa to generate plasma for etching for about 30 seconds. The substrateside (sample stage) also receives an RF power (13.56 MHz) of 20 W toapply a substantially negative self-bias voltage. Under the secondetching conditions where a mixture of CF₄ and Cl₂ is used, the W filmand the TaN film are etched to the same degree. In order to etch thefilms without leaving any residue on the gate insulating film, theetching time is increased by around 10 to 20%.

In the first etching treatment, the first conductive layer and thesecond conductive layer are tapered around their edges by the effect ofthe bias voltage applied to the substrate side if the resist masks haveappropriate shapes. The angle of the tapered portions is 15 to 45°. Inthis way, first shape conductive layers 617 to 622 consisting of thefirst conductive layer and the second conductive layer (first conductivelayers 617 a to 622 a and second conductive layers 617 b to 622 b) areformed through the first etching treatment. Denoted by 616 is a gateinsulating film, and regions of the gate insulating film that are notcovered with the first shape conductive layers 617 to 622 are etched andthinned by about 20 to 50 nm.

Next follows the second etching treatment with the resist masks kept inplace (FIG. 24C). Here, CF₄, Cl₂ and O₂ are used as etching gas to etchthe W film selectively. Second conductive layers 628 b to 633 b areformed through the second etching treatment. On the other hand, thefirst conductive layers 617 a to 622 a are hardly etched in thistreatment and second shape conductive layers 628 to 633 are formed.

Without removing the resist masks, the first doping treatment isconducted to dope the islands with an impurity element that gives then-type conductivity in low concentration. The doping treatment employsion doping or ion implantation. The ion doping conditions includesetting the dose to 1×10¹³ to 5×10¹⁴ atoms/cm² and the accelerationvoltage to 40 to 80 kV. In this embodiment, the dose is set to 1.5×10¹³atoms/cm² and the acceleration voltage is set to 60 kV. An impurityelement that gives the n-type conductivity is an element belonging toGroup 15, typically, phosphorus (P) or arsenic (As). This embodimentemploys phosphorus (P). In this case, the conductive layers 628 to 633serve as masks against the impurity element that gives the n-typeconductivity and impurity regions 623 to 627 are formed in aself-aligning manner. The impurity regions 623 to 627 are doped with theimpurity element that gives the n-type conductivity in a concentrationof 1×10¹⁸ to 1×10²⁰/cm³.

The resist masks are removed and new resist masks 634 a to 634 c areformed for the second doping treatment. The acceleration voltage ishigher in the second doping treatment than in the first dopingtreatment. The ion doping conditions include setting the dose to 1×10¹³to 1×10¹⁵ atoms/cm² and the acceleration voltage to 60 to 120 kV. In thesecond doping treatment, the second conductive layers 628 b to 632 b areused as masks against the impurity element and the islands under thetapered portions of the first conductive layers are doped with theimpurity element. Then, the third doping treatment is carried out withthe acceleration voltage set lower than that in the second dopingtreatment to obtain the state of FIG. 25A. The ion doping conditionsinclude setting the dose to 1×10¹⁵ to 1×10¹⁷ atoms/cm² and theacceleration voltage to 50 to 100 kV. As a result of the second andthird doping treatments, low concentration impurity regions 636, 642,and 648 overlapping the first conductive layers are doped with animpurity element that gives the n-type conductivity in a concentrationof 1×10¹⁸ to 5×10¹⁹/cm³, and high concentration impurity regions 635,641, 644, and 647 are doped with an impurity element that gives then-type conductivity in a concentration of 1×10¹⁹ to 5×10²¹/cm³.

If the acceleration voltage is suitably set, the second doping treatmentand the third doping treatment can be integrated, so that the lowconcentration impurity regions and high concentration impurity regionsare formed in one doping treatment.

Next, the resist masks are removed and new resist masks 650 a to 650 care formed for the fourth doping treatment. Through the fourth dopingtreatment, impurity regions 653, 654, 659, and 660 are formed in theislands that are to serve as active layers of p-channel TFTs. Theimpurity regions 653, 654, 659, and 660 are doped with an impurityelement that gives the conductivity reverse to the n-type conductivity.In the fourth doping treatment, the second conductive layers 628 a to632 a are used as masks against the impurity element. In this way, theimpurity regions doped with an impurity element that gives the p-typeconductivity are formed in a self-aligning manner. The impurity regions653, 654, 659 and 660 in this embodiment are formed by ion doping usingdiborane (B₂H₆) (FIG. 25B). In the fourth doping treatment, the islandsfor forming n-channel TFTs are covered with the resist masks 650 a to650 c. The impurity regions 653, 654, 659, and 660 have been doped withphosphorus by the first through the third doping treatment in differentconcentrations. However, any of the impurity regions is doped in thefourth doping treatment with an impurity element that gives the p-typeconductivity in a concentration of 1×10¹⁹ to 5×10²¹ atoms cm².Therefore, the impurity regions have no problem in functioning as sourceregions and drain regions of p-channel TFTs.

Through the above steps, impurity regions are formed in the respectiveislands.

Next, the resist masks 650 a to 650 c are removed and a first interlayerinsulating film 661 is formed. This first interlayer insulating film 661is an insulating film containing silicon and is formed by plasma CVD orsputtering to a thickness of 100 to 200 nm. In this embodiment, asilicon oxynitride film is formed by plasma CVD to a thickness of 150nm. The first interlayer insulating film 661 is not limited to thesilicon oxynitride film but may be a single layer or laminate of otherinsulating films containing silicon.

Next, a laser irradiation method is used as shown in FIG. 25C foractivation treatment. If laser annealing is chosen, the laser that hasbeen used in crystallization can be employed. In activation, themobility is set to the same level as the mobility in crystallization andthe energy density required is 0.01 to 100 MW/cm² (preferably 0.01 to 10MW/cm²). It is also possible to use a continuous wave laser incrystallization and a pulse oscillation laser in activation.

The activation treatment may be conducted before the first interlayerinsulating film is formed.

Then, thermal processing (heat treatment at 300 to 550° C. for 1 to 12hours) is conducted for hydrogenation. This step is to terminatedangling bonds in the islands using hydrogen that is contained in thefirst interlayer insulating film 661. Examples of alternativehydrogenation means include plasma hydrogenation using hydrogen that isexcited by plasma, and heat treatment conducted in an atmosphere whichcontains 3 to 100% of hydrogen at 300 to 650° C. for 1 to 12 hours. Inthis case, the semiconductor layers can be hydrogenated irrespective ofpresence or absence of the first interlayer insulating film.

On the first interlayer insulating film 661, a second interlayerinsulating film 662 is formed from an inorganic insulating material oran organic insulating material. In this embodiment, an acrylic resinfilm is formed to a thickness of 1.6 μm. Next, a third interlayerinsulating film 672 is formed after the formation of the secondinterlayer insulating film 662 so as to come into contact with thesecond interlayer insulating film 662.

Subsequently, wirings 663 to 668 are formed to be electrically connectedto the respective impurity regions in a driving circuit 686. Thesewirings are formed by patterning a laminate of a 50 nm thick Ti film and500 nm thick alloy film (Al—Ti alloy film). The wirings are not limitedto the two-layer structure and may take a single-layer structure or amulti-layer structure with three or more layers. Wiring materials arenot limited to Al and Ti. For example, the wirings may be formed bypatterning a laminate film in which an Al film or a Cu film is formed ona TaN film and a Ti film is formed thereon (FIG. 26).

In a pixel portion 687, a pixel electrode 670, a gate wiring 669, and aconnection electrode 668 are formed. The connection electrode 668 allowssource wirings (a laminate of 643 a and 643 b) to electrically connectwith a pixel TFT. The gate wiring 669 forms an electrical connectionwith a gate electrode of the pixel TFT. The pixel electrode 670 forms anelectrical connection with a drain region 690 of the pixel TFT andanother electrical connection with an island 685 that functions as oneof electrodes constituting capacitor storage. In this patentapplication, the pixel electrode and the connection electrode are formedfrom the same material. Desirably, the pixel electrode 670 is formedfrom a material having excellent reflectivity, for example, a filmmainly containing Al or Ag, or a laminate of such films.

The driving circuit 686, which has a CMOS circuit composed of ann-channel TFT 681 and a p-channel TFT 682 and has an n-channel TFT 683,and the pixel portion 687, which has a pixel TFT 684 and capacitorstorage 685, can thus be formed on the same substrate. In this way, anactive matrix substrate is completed.

The n-channel TFT 681 of the driving circuit 686 has a channel formationregion 637, the low concentration impurity regions 636 (GOLD (gateoverlapped LDD) region), and high concentration impurity regions 652.The low concentration impurity regions 636 overlap the first conductivelayer 628 a that constitutes a part of a gate electrode. One of the highconcentration impurity regions 652 serves as a source region and theother serves as a drain region. Connected to this n-channel TFT 681through an electrode 666 to form the CMOS circuit is the p-channel TFT682. The p-channel TFT 682 has a channel formation region 640, the highconcentration impurity regions 653, and the impurity regions 654. One ofthe high concentration impurity regions 653 serves as a source regionand the other serves as a drain region. The impurity regions 654 haveintroduced therein an impurity element that gives the p-typeconductivity. The n-channel TFT 683 has a channel formation region 643,the low concentration impurity regions 642 (GOLD regions), and highconcentration impurity regions 656. The low concentration impurityregions 642 overlap the first conductive layer 630 a that constitutes apart of a gate electrode. One of the high concentration impurity regions656 serves as a source region and the other serves as a drain region.

The pixel TFT 684 of the pixel portion has a channel formation region646, the low concentration impurity regions 645 (LDD regions), and highconcentration impurity regions 658. The low concentration impurityregions 645 are formed outside of the gate electrode. One of the highconcentration impurity regions 658 serves as a source region and theother serves as a drain region. The island that serves as one ofelectrodes of the capacitor storage 685 is doped with an impurityelement that gives the n-type conductivity and an impurity element thatgives the p-type conductivity. The capacitor storage 685 is composed ofan electrode (a laminate of 632 a and 632 b) and an island with theinsulating film 616 as dielectric.

According to the pixel structure of this embodiment, edges of a pixelelectrode overlap a source wiring so that the gap between pixelelectrodes is shielded against light without using a black matrix.

This embodiment can be combined with Embodiments 1 through 4.

Embodiment 6

This embodiment describes a process of manufacturing a reflective liquidcrystal display device from the active matrix substrate that ismanufactured in Embodiment 5. The description is given with reference toFIG. 27.

First, an active matrix substrate in the state of FIG. 26 is obtainedfollowing the description in Embodiment 5. On the active matrixsubstrate of FIG. 26, at least on the pixel electrode 670, anorientation film 867 is formed and subjected to rubbing treatment. Inthis embodiment, before forming the orientation film 867, an acrylicresin film or other organic resin film is patterned to form in desiredpositions columnar spacers 872 for keeping the gap between substrates.Instead of the columnar spacers, spherical spacers may be sprayed ontothe entire surface of the substrate.

Next, an opposite substrate 869 is prepared. Colored layers 870 and 871and a planarization film 873 are formed on the opposite substrate 869.The red colored layer 870 and the blue colored layer 871 are overlappedto form a light-shielding portion. Alternatively, a red colored layerand a green colored layer may be partially overlapped to form alight-shielding portion.

This embodiment uses the substrate shown in Embodiment 5. Therefore, atleast the gap between the gate wiring 669 and the pixel electrode 670,the gap between the gate wiring 669 and the connection electrode 668,and the gap between the connection electrode 668 and the pixel electrode670 have to be shielded against light. In this embodiment, the coloredlayers are arranged such that the light-shielding portion that is alaminate of the colored layers overlaps these gaps to be shieldedagainst light. Then, the opposite substrate is bonded.

The number of steps is thus reduced by using a light-shielding portionthat is a laminate of colored layers to shield gaps between pixelsagainst light instead of forming a light-shielding layer such as a blackmask.

Next, a transparent conductive film is formed as an opposite electrode876 on the planarization film 873 at least in the pixel portion. Anorientation film 874 is formed on the entire surface of the oppositesubstrate and is subjected to rubbing treatment.

Then, the opposite substrate is bonded by a seal member 868 to theactive matrix substrate on which the pixel portion and the drivingcircuit are formed. The seal member 868 has fillers mixed therein, andthe fillers together with the columnar spacers keep the gap uniformbetween the two substrates while they are bonded. Thereafter, a liquidcrystal material 875 is injected to the space between the two substratesand the device is completely sealed with a sealing agent (not shown inthe drawing). The liquid crystal material 875 is a known liquid crystalmaterial. In this way, a reflective liquid crystal display device shownin FIG. 27 is completed. If necessary, the active matrix substrate orthe opposite substrate is cut into pieces of desired shapes. Apolarizing plate (not shown in the drawing) is then bonded to theopposite substrate alone. Thereafter, an FPC is bonded by a knowntechnique.

The thus manufactured liquid crystal display device has TFTs formed froma semiconductor film that has crystal grains of large grain size formedthrough irradiation by laser light with periodic or uniform energydistribution. This gives the liquid crystal display device satisfactoryoperation characteristics and reliability. Such liquid crystal displaydevice can be used as a display unit of various electronic equipment.

This embodiment can be combined with Embodiments 1 through 5.

Embodiment 7

This embodiment describes an example of manufacturing a light emittingdevice using the TFT manufacturing method when manufacturing the activematrix substrate shown in Embodiment 5. “Light emitting device” is ageneric term for a display panel in which a light emitting element isformed on a substrate and sealed between the substrate and a covermember, and for a display module obtained by mounting a TFT and the liketo the display panel. A light emitting element has a layer containing anorganic compound that provides luminescence upon application of electricfield (electroluminescence), as well as an anode layer and a cathodelayer. Luminescence obtained from organic compounds is classified intolight emission upon return to the base state from singlet excitation(fluorescence) and light emission upon return to the base state fromtriplet excitation (phosphorescence). The present invention includes oneor both of the two types of light emission.

In this specification, all the layers that are formed between a cathodeand an anode in a light emitting element are collectively defined as anorganic light emitting layer. Specifically, an organic light emittinglayer includes a light emitting layer, a hole injection layer, anelectron injection layer, a hole transporting layer, an electrontransporting layer, etc. The basic structure of a light emitting elementis a laminate of an anode layer, light emitting layer, and cathode layerlayered in this order. The basic structure may be modified into alaminate in which an anode layer, a hole injection layer, a lightemitting layer, a cathode layer, etc. are layered in this order, or alaminate in which an anode layer, a hole injection layer, a lightemitting layer, an electron transporting layer, a cathode layer, etc.are layered in this order.

A light emitting element used in this embodiment may also take a mode inwhich a hole injection layer, an electron injection layer, a holetransporting layer, or an electron transporting layer is formed solelyof an inorganic compound or from a material obtained by mixing aninorganic compound with an organic compound. The layers listed may bepartially mixed with one another.

FIG. 28A is a sectional view of a light emitting device of thisembodiment where manufacturing process is finished up through formationof a third interlayer insulating film 750. In FIG. 28A, a switching TFT733 and a current controlling TFT 734 on a substrate 700 are formed bythe manufacturing method of Embodiment 5. The switching TFT 733 in thisembodiment has a double gate structure in which two channel formationregions are formed. However, the switching TFT 733 may take a singlegate structure having one channel formation region or a structure havingthree or more channel formation regions. The current controlling TFT 734in this embodiment has a single gate structure in which one channelformation region is formed, but it may take a structure having two ormore channel formation regions.

An n-channel TFT 731 and p-channel TFT 732 of a driving circuit on thesubstrate 700 are formed by the manufacturing method of Embodiment 5.The TFTs have a single gate structure in this embodiment, but may take adouble gate structure or a triple gate structure.

The third interlayer insulating film 750 is, in a light emitting device,effective in preventing moisture contained in a second interlayerinsulating film 751 from entering an organic light emitting layer. Whenthe second interlayer insulating film 751 has an organic resin material,forming the third interlayer insulating film 750 is particularlyeffective since organic resin materials contain a lot of moisture.

After the process of Embodiment 5 is finished up through the step offorming the third interlayer insulating film, a pixel electrode 711 isformed on the third interlayer insulating film 750 in this embodiment.

The pixel electrode 711 is a pixel electrode formed from a transparentconductive film (an anode of a light emitting element). The transparentconductive film used may be formed from a compound of indium oxide andtin oxide or a compound of indium oxide and zinc oxide, or from zincoxide alone, tin oxide alone, or indium oxide alone. The transparentconductive film doped with gallium may be used. The pixel electrode 711is formed on the flat third interlayer insulating film 750 beforewirings are formed. In this embodiment, it is very important to use asecond interlayer insulating film 751 formed of a resin to level thelevel differences caused by the TFTs. If there are level differences,they may cause defective light emission since a light emitting layerwhich is formed later is very thin. Accordingly, the surface should beleveled before the pixel electrode is formed, so that the light emittinglayer can be formed on as flat a surface as possible.

Next, as shown in FIG. 28B, a resin film dispersed with black dye,carbon, or black pigments is formed so as to cover the third interlayerinsulating film 750. An opening is formed in the film at a positionwhere a light emitting element is formed. This film serves as alight-shielding film 770. The material of the resin film is typicallypolyimide, polyamide, acrylic, or BCB (benzocyclobutene), but is notlimited thereto. Examples of other light-shielding film materials thanorganic resins include silicon, silicon oxide, silicon oxynitride, andthe like with black dye, carbon, or black pigments mixed therein. Thelight-shielding film 770 has an effect of preventing external lightreflected by wirings 701 to 707 from reaching eyes of a viewer.

After the pixel electrode 711 is formed, contact holes are formed in agate insulating film 752, a first interlayer insulating film 753, thesecond interlayer insulating film 751, the third interlayer insulatingfilm 750, and the light-shielding film 770. Then a conductive film isformed on the light-shielding film 770 to cover the pixel electrode 711.The conductive film is etched to form wirings 701 to 707 that areelectrically connected to impurity regions of the respective TFTs. Thesewirings are formed by patterning a laminate of a 50 nm thick Ti film and500 nm thick alloy film (an alloy of Al and Ti). The wirings are notlimited to the two-layer structure and may take a single-layer structureor a multi-layer structure of three or more layers. Wiring materials arenot limited to Al and Ti. For example, the wirings may be formed bypatterning a laminate film in which an Al film or a Cu film is formed ona TaN film and a Ti film is formed thereon (FIG. 28A).

The wiring 707 is a source wiring (corresponding to a current supplyline) of the current controlling TFT. The wiring 706.1 s an electrodethat electrically connects a drain region of the current controlling TFTwith the pixel electrode 711.

After the wirings 701 to 707 are formed, a bank 712 is formed from aresin material. The bank 712 is formed by patterning acrylic film orpolyimide film with a thickness of 1 to 2 μm so as to expose a part ofthe pixel electrode 711.

A light emitting layer 713 is formed on the pixel electrode 711.Although only one pixel is shown in FIG. 28B, three types of lightemitting layers for R (red), G (green), and B (blue) colors are formedin this embodiment. The light emitting layers in this embodiment areformed by evaporation from low-molecular weight organic light emittingmaterials. Specifically, a copper phthalocyanine (CuPc) film with athickness of 20 nm is formed as a hole injection layer and atris-8-quinolinolate aluminum complex (Alq₃) film is layered thereon asa light emitting layer. The color of emitted light can be controlled bydoping Alq₃ with a fluorescent pigment such as quinacridon, perylene, orDCM1.

However, the materials given in the above are merely examples of organiclight emitting materials that can be used as light emitting layers andthere is no need to exclusively use them. A light emitting layer (alayer in which carriers are moved to thereby emit light) is formed byfreely combining a light emitting layer with an electric chargetransporting layer or an electric charge injection layer. Although alow-molecular weight organic light emitting material is used for a lightemitting layer in the example shown in this embodiment, anintermediate-molecular weight organic light emitting material or ahigh-molecular weight organic light emitting material may be usedinstead. In this specification, an organic light emitting material withno sublimation property in which the number of molecules is 20 or lessand the length of molecular chain is 10 μm or less is called anintermediate-molecular weight organic light emitting material. As anexample of employing a high-molecular weight organic light emittingmaterial, a laminate structure may be adopted in which a polythiophene(PEDOT) film is formed as a hole injection layer by spin coating to athickness of 20 nm and a paraphenylene vinylene (PPV) film with athickness of about 100 nm is layered thereon as a light emitting layer.If a π-conjugate polymer of PPV is used, a light emission wavelengthranging from red to blue can be chosen. Inorganic materials such assilicon carbide can be used for an electric charge transporting layerand an electric charge injection layer. These organic light emittingmaterials and inorganic materials may be known materials.

Next, a cathode 714 is formed from a conductive film on the lightemitting layer 713. In this embodiment, the conductive film is a film ofan alloy of aluminum and lithium. A known MgAg film (a film of an alloyof magnesium and silver) may also be used. It is sufficient if thecathode material is a conductive film formed of an element that belongsto Group 1 or 2 in the periodic table or a conductive film doped withsuch element.

With formation of the cathode 714, a light emitting element 715 iscompleted. The light emitting element 715 here refers to a diodecomposed of the pixel electrode (anode) 711, the light emitting layer713, and the cathode 714.

A protective film 754 may be provided so as to completely cover thelight emitting element 715. A carbon film or insulating films includinga silicon nitride film and a silicon oxynitride film can be used for theprotective film 754, which is a single layer or laminate of those films.

Preferably, a film with good coverage is used as the protective film754. A carbon film, especially DLC (diamond-like carbon) film iseffective. A DLC film can be formed at a temperature ranging from roomtemperature to 100° C. or less and therefore it is easy to form a DLCfilm above the light emitting layer 713, which has low heat resistance.Also, a DLC film has high oxygen blocking effect and is capable ofpreventing oxidization of the light emitting layer 713. Therefore, aproblem of the light emitting layer 713 being oxidized during thesubsequent sealing step can be avoided.

In this embodiment, the light emitting layer 713 is completely coveredwith an inorganic insulating film such as a carbon film, a siliconnitride film, a silicon oxynitride film, an aluminum nitride film, or analuminum oxynitride film, which serves well as a barrier. Therefore,degradation of the light emitting layer due to moisture, oxygen, and thelike seeping into the light emitting layer can be prevented moreeffectively.

Prevention of the intrusion of impurities into the light emitting layerbecomes more thorough if silicon nitride films formed by sputtering withsilicon as the target are used particularly for a third insulating film750, a passivation film 712, and the protective film 754. The filmformation conditions can be suitably chosen. Particularly preferableconditions include using nitrogen (N₂) or a mixture gas of nitrogen andargon as sputtering gas and applying a high-frequency power forsputtering. The substrate temperature is set to room temperature and noheating means is necessary. If an organic insulating film and an organiccompound layer have already been formed, it is desirable to form thesilicon nitride films without heating the substrate. However, heating invacuum for several minutes to several hours at 50 to 100° C. fordehydrogenation treatment is preferable in order to thoroughly removeadsorbed or occluded moisture.

Silicon nitride films formed from nitrogen gas alone by sputtering atroom temperature using silicon as the target and applying a 13.56 MHzhigh-frequency power are characterized in that the absorption peaks ofN—H bond and Si—H bond are not observed in its infrared absorptionspectrum and neither is the absorption peak of Si—O bond, and the oxygenconcentration and hydrogen concentration in these silicon nitride filmsare each 1 atomic % or less. This is another proof of effectiveness ofthe silicon nitride films in preventing the intrusion of impurities suchas oxygen and moisture.

The light emitting element 715 is further covered with a sealing member717 and a cover member 718 is bonded thereto. A UV-curable resin can beused as the sealing member 717 and it is effective to put a hygroscopicmaterial or antioxidant inside the sealing member. The cover member 718used in this embodiment is a glass substrate, quartz substrate, orplastic substrate (or plastic film) with a carbon film (preferablydiamond-like carbon film) formed on each side.

In this way, a light emitting device structured as shown in FIG. 28B iscompleted. As to the steps following formation of the bank 712, it iseffective to process in succession without exposing the device to theair until after the protective film is formed. An advanced version ofthis is to process in succession without exposing the device to the airuntil after the cover member 718 is bonded.

The n-channel TFTs 731 and 732, the switching TFT (n-channel TFT) 733,and the current controlling TFT (n-channel TFT) 734 are thus formed onthe substrate 700.

The light-shielding film 770 is formed between the third interlayerinsulating film 750 and the bank 712 in this embodiment. However, thepresent invention is not limited to this structure. The important thingabout placement of light-shielding film is that it has to be placed insuch a position that can prevent external light reflected by the wirings701 to 707 from reaching eyes of a viewer. For instance, if lightemitted from the light emitting element 715 travels toward the substrate700 side as in this embodiment, the light-shielding film may be placedbetween the first interlayer insulating film 753 and the secondinterlayer insulating film 751. In this case also, the light-shieldingfilm has an opening to let light from the light emitting element to passtherethrough.

As described with reference to FIGS. 28A and 28B, an n-channel TFT thatis not easily degraded by the hot carrier effect can be formed byproviding an impurity region that overlaps a gate electrode with aninsulating film sandwiched therebetween. Therefore, a highly reliablelight emitting device is obtained.

Although this embodiment shows the structures of the pixel portion anddriving circuit alone, logic circuits such as a signal divider circuit,a D/A converter, an operation amplifier, and a γ correction circuit canbe formed on the same insulator in addition to the pixel portion and thedriving circuit by following the manufacturing process of thisembodiment. Furthermore, a memory and a microprocessor can be formed onthe same insulator.

The thus manufactured light emitting device has TFTs formed from asemiconductor film that has crystal grains of large grain size formedthrough irradiation by laser light with periodic or uniform energydistribution. This gives the light emitting device satisfactoryoperation characteristics and reliability. Such light emitting devicecan be used as a display unit of various electronic equipment.

Light emitted from the light emitting element travels toward the TFTside in this embodiment. Alternatively, light from the light emittingelement may travel in the opposite direction of the TFTs. In this case,a resin with black dye, carbon, or black pigments mixed therein can beused for the bank. A sectional view of a light emitting device in whichlight emitted from a light emitting element travels in the oppositedirection of TFTs is shown in FIG. 33.

In FIG. 33, after a third interlayer insulating film 1950 is formed,contact holes are formed in a gate insulating film 1952, a firstinterlayer insulating film 1953, a second interlayer insulating film1951, and the third interlayer insulating film 1950. Then, a conductivefilm is formed on the third interlayer insulating film 1950 and isetched to form wirings 1901 to 1907 that are electrically connected toimpurity regions of the respective TFTs. These wirings are formed bypatterning an aluminum alloy film (an aluminum film containing 1 wt % oftitanium) with a thickness of 300 nm. The wirings are not limited to asingle-layer structure and may take a multi-layer structure having twoor more layers. Wiring materials are not limited to Al and Ti. A part ofthe wiring 1906 doubles as a pixel electrode.

After the wirings 1901 to 1907 are formed, a bank 1912 is formed from aresin material. The bank 1912 is formed by patterning a resin film withblack dye, carbon, or black pigments mixed therein, having a thicknessof 1 to 2 μm so as to expose a part of the pixel electrode 1906. Thematerial of the resin film is typically polyimide, polyamide, acrylic,or BCB (benzocyclobutene), but is not limited thereto.

A light emitting layer 1913 is formed on the pixel electrode 1906. Then,an opposite electrode (an anode of a light emitting element) is formedfrom a transparent conductive material to cover the light emitting layer1913. The transparent conductive film used may be formed from a compoundof indium oxide and tin oxide or a compound of indium oxide and zincoxide, or from zinc oxide alone, tin oxide alone, or indium oxide alone.The transparent conductive film may be doped with gallium.

The pixel electrode 1906, the light emitting layer 1913, and an oppositeelectrode 1914 constitute a light emitting element 1915.

A light-shielding film 1970 has an effect of preventing external lightreflected by the wirings 1901 to 1907 from reaching eyes of a viewer.

This embodiment can be combined with any one of Embodiments 1 through 6.

Embodiment 8

This embodiment describes the structure of a pixel in a light emittingdevice that is one of semiconductor devices of the present invention. Asectional view of a pixel in a light emitting device of this embodimentis shown in FIG. 29.

In FIG. 29, 911 denotes a substrate and 912 denotes an insulating filmthat serves as a base (hereinafter referred to as base film). Thesubstrate 911 is a light-transmissive substrate, typically, a glasssubstrate, a quartz substrate, a glass ceramic substrate, or acrystallized glass substrate. However, one that can withstand thehighest processing temperature of the manufacturing process has to bechosen.

Denoted by 8201 is a switching TFT that is an n-channel TFT and 8202 isa current controlling TFT that is a p-channel TFT. When light is emittedfrom an organic light emitting layer toward the bottom face of asubstrate (the side where TFTs and the organic light emitting layer arenot formed), the above structure is preferred. However, the switchingTFT and the current controlling TFT each can assume both conductivitytypes and therefore 8201 may be a p-channel TFT and 8202 may be ann-channel TFT.

The switching TFT 8201 has an active layer, a gate insulating film 918,gate electrodes 919 a and 919 b, a first interlayer insulating film 920,a source signal line 921, and a drain wiring 922. The active layerincludes a source region 913, a drain region 914, LDD regions 915 a to915 d, a divider region 916 and channel formation regions 963 and 964.The gate insulating film 918 or the first interlayer insulating film 920may be common to all TFTs on the substrate, or different circuits orelements may have different gate insulating films or different firstinterlayer insulating films.

In the switching TFT 8201 shown in FIG. 29, the gate electrodes 917 aand 917 b are electrically connected to each other to form a double-gatestructure. The switching TFT 8201 may take other multi-gate structure (astructure including an active layer that has two or more channelformation regions connected in series) than the double-gate structure,such as a triple-gate structure.

A multi-gate structure is very effective in reducing OFF current. If OFFcurrent of the switching TFT is lowered enough, the minimum capacitancerequired for capacitor storage that is connected to a gate electrode ofthe current controlling TFT 8202 can be reduced that much. In otherwords, it reduces the area of the capacitor storage. It is thereforeeffective to employ a multi-gate structure in increasing the effectivelight emission area of a light emitting element.

Furthermore, the LDD regions 915 a to 915 d in the switching TFT 8201are placed so as to avoid overlap of the LDD regions and the gateelectrodes 919 a and 919 b with the gate insulating film 918 sandwichedtherebetween, and this structure is very effective in reducing OFFcurrent. The length (width) of each of the LDD regions 915 a to 915 d isset to 0.5 to 3.5 μm, typically, 2.0 to 2.5 μm. In a multi-gatestructure having two or more gate electrodes, the divider region 916 (aregion doped with the same impurity element in the same concentration asthe source region or the drain region) provided between the channelformation regions is effective in lowering OFF current.

The current controlling TFT 8202 has an active layer, the gateinsulating film 918, a gate electrode 930, the first interlayerinsulating film 920, a source signal line 931, and a drain wiring 932.The active layer includes a source region 926, a drain region 927, and achannel formation region 905. The current controlling TFT 8202 in thisembodiment is a p-channel TFT.

The drain region 914 of the switching TFT 8201 is connected to the gateelectrode 930 of the current controlling TFT 8202. Specifically, thoughnot shown in the drawing, the gate electrode 930 of the currentcontrolling TFT 8202 is electrically connected through the drain wiring(also called a connection wiring) 922 to the drain region 914 of theswitching TFT 8201. The gate electrode 930 has a single gate structurebut may have a multi-gate structure. The source, signal line 931 of thecurrent controlling TFT 8202 is connected to a power supply line (notshown in the drawing).

The description given above is about the structures of the TFTs providedin the pixel. At the same time the TFTs are formed, a driving circuit isalso formed. Shown in FIG. 29 is a CMOS circuit that is the basic unitconstituting the driving circuit.

In FIG. 29A, a TFT structured to reduce hot carrier injection whileavoiding slowing the operation speed as much as possible is used as ann-channel TFT 8204 of the CMOS circuit. The driving circuit here refersto a source signal side driving circuit or a gate signal side drivingcircuit. Other logic circuits (such as a level shifter, an A/Dconverter, and a signal divider circuit) may also be formed.

An active layer of the n-channel TFT 8204 of the CMOS circuit includes asource region 935, a drain region 936, an LDD region 937, and a channelformation region 962. The LDD region 937 overlaps a gate electrode 939with the gate insulating film 918 sandwiched therebetween.

The LDD region 937 is formed only on the drain region 936 side becauseit prevents slowing of the operation speed. In the n-channel TFT 8204,the OFF current value is not so important and rather the operation speedshould be given priority. Accordingly, it is desirable if the LDD region937 overlaps the gate electrode completely to reduce the resistancecomponent as much as possible. In other words, eliminating offset ispreferred.

In a p-channel TFT 8205 of the CMOS circuit, degradation by hot carrierinjection is almost ignorable and therefore has no particular need foran LDD region. Accordingly, its active layer includes a source region940, a drain region 941, and a channel formation region 961. The gateinsulating film 918 and a gate electrode 943 are provided under theactive layer. It is also possible for the p-channel TFT 8205 to have anLDD region as a countermeasure for hot carrier as in the n-channel TFT8204.

Denoted by 942, 938, 917 a, 917 b, and 929 are masks for forming thechannel formation regions 961 to 965.

The n-channel TFT 8204 and the p-channel. TFT 8205 have above theirsource regions a source signal line 944 and a source signal line 945,respectively, with first interlayer insulating films 920 (or the firstinterlayer insulating film 920) sandwiched between the source regionsand the source signal lines. The drain regions of the n-channel TFT 8204and p-channel TFT 8205 are electrically connected to each other by adrain wiring 946.

A laser irradiation method of the present invention can be used information of the semiconductor film, crystallization of the activelayers, activation, and other steps where laser annealing is used.

FIG. 30 shows production flow for manufacturing the light emittingdevice of this embodiment. First, a semiconductor device is designedusing CAD. Specifically, a mask for an island is designed first and thena mask for a sub-island that includes one or more of such islands isdesigned.

Then, information concerning the shape of the designed mask for asub-island (pattern information) is inputted to a computer of laserirradiation apparatus. From the sub-island pattern information inputted,the computer calculates a width W_(S) of each sub-island in thedirection perpendicular to the scanning direction. Based on the widthW_(S) of each sub-island, a slit width W_(BW) in the directionperpendicular to the scanning direction is set. The laser light scanningpath is determined from the slit width W_(BW) with the position of amarker as the reference.

During this, a gate electrode is formed in accordance with the markerformed on a substrate. Alternatively, the gate electrode and the markermay be formed at the same time. Then a gate insulating film is formed soas to cover the gate electrode and a semiconductor film is formed so asto come into contact with the gate insulating film. The semiconductorfilm is patterned using the mask for a sub-island to form a sub-island.The substrate on which the sub-island is formed is set on a stage of thelaser irradiation apparatus.

With the marker as the reference, laser light is irradiated along theset scanning path targeting the sub-island to crystallize thesub-island.

Thereafter, the sub-island having its crystallinity enhanced by thelaser light irradiation is patterned to form an island. Subsequently, aprocess of manufacturing a TFT from the island follows. Althoughspecifics of the TFT manufacturing process are varied depending on theTFT form, a typical process starts with forming an impurity region inthe island. Then an interlayer insulating film is formed so as to coverthe island. A contact hole is formed in the interlayer insulating filmto partially expose the impurity region. A wiring is then formed on theinterlayer insulating film to reach the impurity region through thecontact hole.

The structure of this embodiment can be combined freely with Embodiments1 through 7.

Embodiment 9

This embodiment describes the structure of a pixel in a light emittingdevice that is manufactured using a laser irradiation method of thepresent invention. A sectional view of a pixel in a light emittingdevice of this embodiment is shown in FIG. 31.

Denoted by 1751 is an n-channel TFT and 1752, a p-channel TFT. Then-channel TFT 1751 has a semiconductor film 1753, a first insulatingfilm 1770, first electrodes 1754 and 1755, a second insulating film1771, and second electrodes 1756 and 1757. The semiconductor film 1753has a first concentration one conductivity type impurity region 1758, asecond concentration one conductivity type impurity region 1759, andchannel formation regions 1760 and 1761.

The first electrodes 1754 and 1755 overlap the channel formation regions1760 and 1761, respectively, with the first insulating film 1770sandwiched between the first electrodes and the channel formationregions. The second electrodes 1756 and 1757 overlap the channelformation regions 1760 and 1761, respectively, with the secondinsulating film 1771 sandwiched between the second electrodes and thechannel formation regions.

The p-channel TFT 1752 has a semiconductor film 1780, the firstinsulating film 1770, a first electrode 1782, the second insulating film1771, and a second electrode 1781. The semiconductor film 1780 has athird concentration one conductivity type impurity region 1783 and achannel formation region 1784.

The first electrode 1782 overlaps the channel formation region 1784 withthe first insulating film 1770 sandwiched therebetween. The secondelectrode 1781 overlaps the channel formation region with the secondinsulating film 1771 sandwiched therebetween.

The first electrode 1782 and the second electrode 1781 are electricallyconnected to each other through a wiring 1790.

A laser irradiation method of the present invention can be used information of the semiconductor films 1753 and 1780, crystallization,activation, and other steps where laser annealing is used.

In this embodiment, a constant voltage is applied to the first electrodeof the TFT used as a switching element (here, the n-channel TFT 1751).By applying a constant voltage to the first electrode, fluctuation inthreshold can be reduced and OFF current can be lowered compared to thecase where the TFT has only one electrode.

In the TFT (the p-channel TFT 1752 in this embodiment) where a largercurrent flows compared to the TFT used as a switching element, the firstelectrode and the second electrode are electrically connected to eachother. By applying the same voltage to the first electrode and thesecond electrode, the depletion layer spreads quickly as though thesemiconductor film is actually reduced in thickness. Therefore thesub-threshold coefficient can be reduced and ON current can beincreased. Accordingly, when used in a driving circuit, the TFTstructured as this can lower the drive voltage. An increase in ONcurrent leads to reduction in size (channel width, in particular) of theTFT. As a result, the integration density can be improved.

FIG. 32 shows production flow for manufacturing the light emittingdevice of this embodiment. First, a semiconductor device is designedusing CAD. Specifically, a mask for an island is designed first and thena mask for a sub-island that includes one or more of such islands isdesigned. Then the designed pattern information of a sub-island isinputted to a computer of laser irradiation apparatus.

From the sub-island pattern information inputted, the computercalculates a width W_(S) of each sub-island in the directionperpendicular to the scanning direction. Based on the width W_(S) ofeach sub-island, a slit width W_(BW) in the direction perpendicular tothe scanning direction is set. The laser light scanning path isdetermined from the slit width W_(BW) with the position of a marker asthe reference.

During this, a first gate electrode is formed in accordance with themarker formed on a substrate. Alternatively, the first gate electrodeand the marker may be formed at the same time. Then a first insulatingfilm is formed so as to cover the first gate electrode and asemiconductor film is formed so as to come into contact with the firstinsulating film. The semiconductor film is patterned using the mask fora sub-island to form a sub-island. The substrate on which the sub-islandis formed is set on a stage of the laser irradiation apparatus.

With the marker as the reference, laser light runs along the setscanning path targeting the sub-island to crystallize the sub-island.

Thereafter, the sub-island having its crystallinity enhanced by thelaser light irradiation is patterned to form an island. Subsequently, aprocess of manufacturing a TFT from the island follows. Althoughspecifics of the TFT manufacturing process are varied depending on theTFT form, a typical process starts with forming an impurity region inthe island. Then laser irradiation follows and a second insulating filmand a second electrode are sequentially formed so as to cover theisland. An impurity region is formed in the island. An interlayerinsulating film is then formed so as to cover the second insulating filmand the second electrode. A contact hole is formed in the interlayerinsulating film to partially expose the impurity region. A wiring isthen formed on the interlayer insulating film to reach the impurityregion through the contact hole.

This embodiment can be combined with any one of Embodiments 1 through 8.

Embodiment 10

This embodiment describes an example in which a driving circuit (asignal line driving circuit or a scanning line driving circuit) isformed by using a laser irradiation method of the present invention andis mounted to a pixel portion formed from an amorphous semiconductorfilm using TAB, COG, or the like.

FIG. 40A shows an example of mounting a driving circuit to a TAB tape sothat a pixel portion is connected by the TAB tape to a printed substrateon which an external controller and others are formed. A pixel portion5001 is formed on a glass substrate 5000, and is connected through a TABtape 5005 to a driving circuit 5002 that is manufactured by a laserirradiation method of the present invention. The driving circuit 5002 isconnected through the TAB tape 5005 to a printed substrate 5003. Theprinted substrate 5003 has a terminal 5004 for connecting the substrateto an external interface.

FIG. 40B shows an example of mounting a driving circuit and a pixelportion by COG. A pixel portion 5101 is formed on a glass substrate5100, and a driving circuit 5102 manufactured by a laser irradiationmethod of the present invention is mounted to the glass substrate. Thesubstrate 5100 has a terminal 5104 for connecting the substrate to anexternal interface.

As described, a TFT manufactured by a laser irradiation method of thepresent invention is improved in crystallinity of its channel formationregion and therefore can operate at high speed. The TFT is thereforesuitable for constituting a driving circuit which is required to operateat higher speed than a pixel portion. If the pixel portion and thedriving circuit are manufactured separately, the yield is increased.

This embodiment can be combined with any one of Embodiments 1 through 9.

Embodiment 11

This embodiment describes a method of manufacturing a TFT using a laserirradiation method of the present invention.

First, as shown in FIG. 34A, an amorphous semiconductor film is formedon an insulating surface and etched to form island-like semiconductorfilms 6001 and 6002. FIG. 34G is a top view of FIG. 34A, and a sectionalview taken along the line A-A′ corresponds to FIG. 34A. Next, as shownin FIG. 34B, an amorphous semiconductor film 6003 is formed so as tocover the island-like semiconductor films 6001 and 6002. FIG. 34H is atop view of FIG. 34B, and a sectional view taken along the line A-A′corresponds to FIG. 34B.

The amorphous semiconductor film 6003 is then patterned as shown in FIG.34C to form a sub-island 6004 that covers the island-like semiconductorlayers 6001 and 6002. FIG. 34I is a top view of FIG. 34C, and asectional view taken along the line A-A′ corresponds to FIG. 34C. Next,the island-like semiconductor layers 6001 and 6002 and the sub-island6004 are selectively irradiated with laser light as shown in FIG. 34D toform island-like semiconductor films 6005 and 6006 and sub-island 6007with improved crystallinity. The borders between the island-likesemiconductor films 6005 and 6006 and sub-island 6007 with improvedcrystallinity may not be clear depending on laser light irradiationconditions. Here, they are distinguished from one another but may bedeemed as one sub-island. FIG. 34J is a top view of FIG. 34D, and asectional view taken along the line A-A′ corresponds to FIG. 34D.

The sub-island 6007 with improved crystallinity is then patterned asshown in FIG. 34E to form an island 6008. FIG. 34K is a top view of FIG.34E, and a sectional view taken along the line A-A′ corresponds to FIG.34E. A TFT is formed from the island 6008 as shown in FIG. 34F.Specifics of the TFT manufacturing process that follows are varieddepending on the TFT form. However, a typical process includes forming agate insulating film 6009 so as to come into contact with the island6008, forming a gate electrode 6010 on the gate insulating film, formingimpurity regions 6011 and 6012 and a channel formation region 6013 inthe island 6008, forming an interlayer insulating film 6014 to cover thegate insulating film 6009, the gate electrode 6010, and the island 6008,and forming wirings 6015 and 6016 on the interlayer insulating film 6014to connect the wirings to the impurity regions 6011 and 6012. FIG. 34Lis a top view of FIG. 34F, and a sectional view taken along the lineA-A′ corresponds to FIG. 34F.

The impurity regions 6011 and 6012 are composed of the island-likesemiconductor films 6005 and 6006 and a part of the island 6008.Therefore the impurity regions 6011 and 6012 are thicker than thechannel formation region 6013 and the resistance of the impurity regionscan be lowered.

Although the sub-island is crystallized by laser light alone in FIGS.34A to 34L, a step of crystallizing the semiconductor films using acatalytic element may be added.

A method of forming an island using a catalytic element and laser lightboth is described with reference to FIGS. 35A to 35G. In using acatalytic element, it is desirable to employ techniques disclosed in JP07-130652 A and JP 08-78329 A.

First, as shown in FIG. 35A, an amorphous semiconductor film is formedon an insulating surface and etched to form island-like semiconductorfilms 6101 and 6102. Next, as shown in FIG. 35B, an amorphoussemiconductor film 6103 is formed so as to cover the island-likesemiconductor films 6101 and 6102. As shown in FIG. 35C, a nickelacetate solution containing 10 ppm of nickel by weight is applied to theamorphous semiconductor film 6103 to form a nickel-containing layer.After a dehydrogenation step at 500° C. for an hour, the amorphoussemiconductor film is subjected to heat treatment at 500 to 650° C. for4 to 12 hours, for example, at 550° C. for 8 hours, for crystallizationto obtain island-like semiconductor films 6104 and 6105 andsemiconductor film 6106 with improved crystallinity. Examples of otheremployable catalytic elements than nickel (Ni) include elements such asgermanium (Ge), iron (Fe), palladium (Pd), tin (Sn), lead (Pb), cobalt(Co), platinum (Pt), copper (Cu), and gold (Au).

The semiconductor film 6106 and the island-like semiconductor films 6104and 6105 contain the catalytic element, which is removed from thecrystalline semiconductor films by gettering. For gettering, a techniquedisclosed in JP 10-135468 A or JP 10-135469 A can be employed. As shownin FIG. 35D, portions of the semiconductor film 6106 with improvedcrystallinity, regions 6107 and 6108, are doped with phosphorus and thensubjected to heat treatment in a nitrogen atmosphere at 550 to 800° C.for 5 to 24 hours, for example, at 600° C. for 12 hours. This causes thephosphorus-doped regions 6107 and 6108 to act as gettering sites, sothat nickel present in the semiconductor film 6106 and in theisland-like semiconductor films 6104 and 6105 is moved to thephosphorus-doped regions and segregated. After that, thephosphorus-doped regions of the polycrystalline semiconductor films areremoved by patterning to obtain an island in which the catalytic elementconcentration is reduced down to 1×10¹⁷ atoms/cm³ or less, preferably,1×10¹⁶ atoms/cm³ or less.

Next, the island-like semiconductor films that have received getteringare patterned as shown in FIG. 35E to form a sub-island 6109. Thesub-island 6109 is selectively irradiated with laser light as shown inFIG. 35F to improve its crystallinity even more. The sub-island 6109with improved crystallinity is then patterned to form an island 6110.

The description given next with reference to FIGS. 36A to 36G is aboutanother method of forming an island using a catalytic element and laserlight both.

First, as shown in FIG. 36A, an amorphous semiconductor film is formedon an insulating surface and etched to form island-like semiconductorfilms 6201 and 6202. Next, as shown in FIG. 36B, an amorphoussemiconductor film 6203 is formed so as to cover the island-likesemiconductor films 6201 and 6202. The amorphous semiconductor film 6203is patterned as shown in FIG. 36C to form a sub-island. A nickel acetatesolution containing 10 ppm of nickel by weight is applied to thesub-island to form a nickel-containing layer. The sub-island is thenirradiated with laser light and heated to form island-like semiconductorfilms 6204 and 6205 and sub-island 6206 with improved crystallinity.Examples of other employable catalytic elements than nickel (Ni) includeelements such as germanium (Ge), iron (Fe), palladium (Pd), tin (Sn),lead (Pb), cobalt (Co), platinum (Pt), copper (Cu), and gold (Au).

The sub-island 6206 and the island-like semiconductor films 6204 and6205 contain the catalytic element, which is removed from thecrystalline semiconductor films by gettering.

As shown in FIG. 36D, a barrier layer 6207 mainly containing silicon isformed on the sub-island 6206. A very thin film can serve as the barrierlayer 6207 and it may be a natural oxide film. Alternatively, thebarrier layer may be an oxide film oxidized by generating ozone throughultraviolet irradiation in an atmosphere containing oxygen. It is alsopossible to use as the barrier layer 6207 an oxide film oxidized by anozone-containing solution that is used in surface treatment calledhydro-washing for removing carbon, i.e., organic substances. The barrierlayer 6207 mainly serves as an etching stopper. Formation of the barrierlayer 6207 may be followed by channel doping and then irradiation withintense light for activation.

Next, a second semiconductor film 6208 is formed on the barrier layer6207. The second semiconductor film 6208 may be a semiconductor filmhaving an amorphous structure or a semiconductor film having acrystalline structure. The thickness of the second semiconductor film6208 is set to 5 to 50 nm, preferably, 10 to 20 nm. It is desirable forthe second semiconductor film 6208 to contain oxygen (in a concentrationof 5×10¹⁸/cm³ or more, preferably 1×10¹⁹/cm³ or more according to SIMS)in order to improve the gettering efficiency.

Formed on the second semiconductor film 6208 is a third semiconductorfilm (gettering site) 6209 containing a rare gas element. The thirdsemiconductor film 6209 may be a semiconductor film with an amorphousstructure which is formed by plasma CVD, reduced pressure thermal CVD,or sputtering, or may be a semiconductor film having a crystallinestructure. The third semiconductor film may contain a rare gas elementwhen it is being formed into a film. Alternatively, a semiconductor filmwhich does not contain a rare gas element at the time of its formationmay be doped with a rare gas element and used as the third semiconductorfilm. The third semiconductor film 6209 in this embodiment has containeda rare gas element since its formation and is further doped with a raregas element by selective doping. (FIG. 36E) The second semiconductorfilm and the third semiconductor film may be formed in successionwithout exposing them to the air. The sum of the thicknesses of thesecond semiconductor film and third semiconductor film is set to 30 to200 nm, for example, 50 nm.

In this embodiment, the third semiconductor film (gettering site) 6209is distanced from the sub-island 6206 and the island-like semiconductorfilms 6204 and 6205 by the second semiconductor film 6208. Duringgettering, a metal or other impurities present in the sub-island 6206and in the island-like semiconductor films 6204 and 6205 tend to gathernear the border of the gettering site. Therefore, the border of thegettering site is desirably distanced from the sub-island 6206 and theisland-like semiconductor films 6204 and 6205 by the secondsemiconductor film 6208 as in this embodiment to improve the getteringefficiency. In addition, the second semiconductor film 6208 has aneffect of blocking impurity elements that are contained in the getteringsite to prevent them from diffusing and reaching the interface of thesub-island 6206 during gettering. Another effect of the secondsemiconductor film 6208 is protection of the sub-island 6206 againstdamage by doping of a rare gas element.

Next, gettering is carried out. Gettering is achieved by heat treatmentin a nitrogen atmosphere at 450 to 800° C. for 1 to 24 hours, forexample, at 550° C. for 14 hours. The heat treatment may be replaced byirradiation with intense light. Alternatively, heat treatment plusintense light irradiation may be employed. Another option is to heat thesubstrate by spraying heated gas. In this case, it is sufficient if thesubstrate is heated at 600 to 800° C., desirably 650 to 750° C., for 1to 60 minutes and the gettering time can be shortened. Through thegettering, the impurity elements move in the direction indicated by thearrow in FIG. 36F. As a result, the impurity elements contained in thesub-island 6206 and island-like semiconductor films 6204 and 6205 whichare covered with the barrier layer 6207 are removed, or theconcentration of the impurity elements in the sub-island and theisland-like semiconductor films is lowered. Here, all of the impurityelements are moved into the third semiconductor film 6209 whilepreventing the impurity elements from segregating in the sub-island 6206and the island-like semiconductor films 6204 and 6205. The sub-island6206 and the island-like semiconductor films 6204 and 6205 shouldreceive thorough gettering so that almost none of the impurity elementsare left in the sub-island 6206 and the island-like semiconductor films6204 and 6205, in other words, so that the impurity elementconcentration in the films becomes 1×10¹⁸/cm³ or less, desirably1×10¹⁷/cm³ or less.

Next, the barrier layer 6207 is used as an etching stopper toselectively remove semiconductor films 6208 and 6209 alone. Then thesub-island 6206 is patterned by a known patterning technique to form anisland 6210 with a desired shape. (FIG. 36G)

This embodiment can be combined with any one of Embodiments 1 through10.

Embodiment 12

This embodiment gives a description on the structure of a TFT formed byusing a laser irradiation method of the present invention.

A TFT shown in FIG. 37A has an active layer that includes a channelformation region 7001, first impurity regions 7002, and second impurityregions 7003. The first impurity regions 7002 sandwich the channelformation region 7001. The second impurity regions 7003 are formedbetween the first impurity regions 7002 and the channel formation region7001. The TFT also has a gate insulating film 7004 that is in contactwith the active layer and a gate electrode 7005 that is formed on thegate insulating film. Side walls 7006 are formed by the gate electrodeand in contact with the side faces of the gate electrode.

The side walls 7006 overlap the second impurity regions 7003 with thegate insulating film 7004 sandwiched between the side walls and thesecond impurity regions. The side walls 7006 may be conductive orinsulative. When the side walls 7006 are conductive, the side walls 7006may constitute a part of the gate electrode.

A TFT shown in FIG. 37B has an active layer that includes a channelformation region 7101, first impurity regions 7102, and second impurityregions 7103. The first impurity regions 7102 sandwich the channelformation region 7101. The second impurity regions 7103 are formedbetween the first impurity regions 7102 and the channel formation region7101. The TFT also has a gate insulating film 7104 that is in contactwith the active layer and a gate electrode that is formed on the gateinsulating film. The gate electrode is a laminate of two conductivefilms 7105 and 7106. Side walls 7107 are formed on the conductive layer7105 and by the conductive layer 7106 so that the side walls are incontact with the top face of 7105 and the side faces of 7106.

The side walls 7107 may be conductive or insulative. When the side walls7107 are conductive, the side walls 7107 may constitute a part of thegate electrode.

A TFT shown in FIG. 37C has an active layer that includes a channelformation region 7201, first impurity regions 7202, and second impurityregions 7203. The first impurity regions 7202 sandwich the channelformation region 7201. The second impurity regions 7203 are formedbetween the first impurity regions 7202 and the channel formation region7201. The TFT also has a gate insulating film 7204 that is in contactwith the active layer. A conductive film 7205 is formed on the gateinsulating film. A conductive film 7206 covers the top and side faces ofthe conductive film 7205. Side walls 7207 are formed by the conductivefilm 7206 and in contact with the side faces of the conductive film7206. The conductive films 7205 and 7206 function as a gate electrode.

The side walls 7207 may be conductive or insulative. When the side walls7207 are conductive, the side walls 7207 may constitute a part of thegate electrode.

This embodiment can be combined with any one of Embodiments 1 through11.

Embodiment 13

The structure of a pixel in a light emitting device of the presentinvention will be described with reference to FIG. 41.

In FIG. 41, a base film 6001 is formed on a substrate 6000 and atransistor 6002 is formed on the base film 6001. The transistor 6002 hasan active layer 6003, a gate electrode 6005, and a gate insulating film6004, which is sandwiched between the active layer 6003 and the gateelectrode 6005.

The active layer 6003 is preferably a polycrystalline semiconductorfilm, and the polycrystalline semiconductor film can be formed by alaser irradiation apparatus of the present invention.

The active layer may be formed of silicon germanium other than silicon.When silicon germanium is employed, the germanium concentration ispreferably about 0.01 to 4.5 atomic %. Silicon doped with carbon nitridemay also be used.

The gate insulating film 6004 can be formed from silicon oxide, siliconnitride, or silicon oxynitride. A silicon oxide film, a silicon nitridefilm, and a silicon oxynitride film may be layered to form the gateinsulating film. For example, a SiN film laid on a SiO₂ film can beused. A silicon oxide film is formed by plasma CVD in which TEOS(tetraethyl orthosilicate) and O₂ are mixed, the reaction pressure isset to 40 Pa, the substrate temperature is set to 300 to 400° C., andthe high frequency (13.56 MHz) power density is set to 0.5 to 0.8 W/cm²for electric discharge. The thus formed silicon oxide film can provideexcellent characteristics as a gate insulating film if it subsequentlyreceives thermal annealing at 400 to 500° C. The gate insulating filmmay also be formed of aluminum nitride. Aluminum nitride has relativelyhigh heat conductivity and is capable of diffusing heat generated in theTFT effectively. A laminate obtained by laying an aluminum nitride filmon a silicon oxide film, a silicon oxynitride film, or the like whichdoes not contain aluminum may also be used as the gate insulating film.It is also possible to employ a SiO₂ film formed by RF sputtering withSi as the target for the gate insulating film.

The gate electrode 6005 is formed of an element selected from the groupconsisting of Ta, W, Ti, Mo, Al, and Cu, or an alloy or compound mainlycontaining the above elements. Alternatively, the gate electrode may bea semiconductor film, typically polycrystalline silicon film, doped withphosphorus or other impurity elements. Instead of a single-layerconductive film, a laminate of plural conductive films may be used asthe gate electrode.

The following are examples of a preferred combination of conductivefilms: a combination of a tantalum nitride (TaN) film as the firstconductive film and a W film as the second conductive film, acombination of a tantalum nitride (TaN) film as the first conductivefilm and a Ti film as the second conductive film, a combination of atantalum nitride (TaN) film as the first conductive film and an Al filmas the second conductive film, and a combination of a tantalum nitride(TaN) film as the first conductive film and a Cu film as the secondconductive film. Alternatively, the first conductive film and the secondconductive film may be semiconductor films, typically polycrystallinesilicon films, doped with phosphorus or other impurities, or may beAg—Pd—Cu alloy films.

The gate electrode is not limited to the two-layer structure. Forexample, a three-layer structure consisting of a tungsten film,aluminum-silicon alloy (Al—Si) film, and titanium nitride film layeredin this order may be employed. When the three-layer structure isemployed, the tungsten film may be replaced by a tungsten nitride film,the aluminum-silicon alloy (Al—Si) film may be replaced by analuminum-titanium alloy (Al—Ti) film, and the titanium nitride film maybe replaced by a titanium film.

It is important to select the optimum etching method and etchant for theconductive film material employed.

The transistor 6002 is covered with a first interlayer insulating film6006. A second interlayer insulating film 6007 and a third interlayerinsulating film 6008 are layered on the first interlayer insulating film6006.

The first interlayer insulating film 6006 is a single layer or laminateof a silicon oxide film, silicon nitride film, and silicon oxynitridefilm formed by plasma CVD or sputtering. A laminate obtained by laying asilicon oxynitride film in which oxygen is higher in mole fraction thannitrogen on top of a silicon oxynitride film in which nitrogen is higherin mole fraction than oxygen may also be used as the first interlayerinsulating film 6006.

If thermal processing (heat treatment at 300 to 550° C. for 1 to 12hours) is conducted after the first interlayer insulating film 6006 isformed, dangling bonds of semiconductors in the active layer 6003 can beterminated (hydrogenated) by hydrogen contained in the first interlayerinsulating film 6006.

The second interlayer insulating film 6007 can be formed ofnon-photosensitive acrylic.

Used as the third interlayer insulating film 6008 should be a film thatdoes not easily transmit moisture, oxygen, and other substances thataccelerate degradation of a light emitting element compared to the otherinsulating films. Typically, a DLC film, a carbon nitride film, asilicon nitride film formed by RF sputtering, or the like is desirablyused as the third interlayer insulating film.

In FIG. 41, denoted by 6010 is an anode, 6011, an electric field lightemitting layer, and 6012, a cathode. An area where the anode 6010, theelectric field light emitting layer 6011, and the cathode 6012 overlapcorresponds to a light emitting element 6013. The transistor 6002 is adriving transistor for controlling a current supplied to the lightemitting element 6013, and is connected to the light emitting element6013 directly or in series through another circuit element.

The electric field light emitting layer 6011 may be a light emittinglayer alone or a laminate of plural layers including a light emittinglayer.

The anode 6010 is formed on the third interlayer insulating film 6008.Also formed on the third interlayer insulating film 6008 is an organicresin film 6014, which is used as a partition wall. The organic resinfilm 6014 has an opening 6015 where the anode 6010, the electric fieldlight emitting layer 6011, and the cathode 6012 overlap to form thelight emitting element 6013.

A protective film 6016 is formed on the organic resin film 6014 and thecathode 6012. Used as the protective film 6016 is, similar to the thirdinterlayer insulating film 6008, a film that does not easily transmitmoisture, oxygen, and other substances that accelerate degradation of alight emitting element compared to the other insulating films.Typically, a DLC film, a carbon nitride film, a silicon nitride filmformed by RF sputtering, or the like is used as the protective film. Itis also possible to use as the protective film a laminate of theabove-described film that does not easily transmit moisture, oxygen, andother substances and a film that transmits moisture, oxygen, and othersubstances easily compared to the former film.

Before the electric field light emitting layer 6011 is formed, theorganic resin film 6014 is heated in a vacuum atmosphere to removeadsorbed moisture, oxygen, and the like. Specifically, heat treatment isconducted in a vacuum atmosphere at 100 to 200° C. for about 0.5 to 1hour. The pressure is set to desirably 3×10⁻⁷ Torr or lower, ifpossible, 3×10⁻⁸ Torr or lower is the best. When the electric fieldlight emitting layer is formed, after the heat treatment of the organicresin film in a vacuum atmosphere, the vacuum atmosphere is maintaineduntil the last moment before the electric field light emitting layer isformed. This enhances the reliability even more.

The end of the organic resin film 6014 in the opening 6015 is desirablyrounded in order to prevent the end from poking a hole in the electricfield light emitting layer 6011 that is formed on the organic resin film6014 and partially overlaps the organic resin film. To be specific, theradius of curvature of the curved organic resin film in section in theopening is desirably about 0.2 to 2 μm.

The above structure gives the electric field light emitting layer andcathode formed later an excellent coverage and can avoid a situationwhere a hole is formed in the electric field light emitting layer 6011and causes short circuit of the anode 6011 and the cathode 6012. Adefect called shrink which refers to reduction of the light emittingregion can be reduced by relieving the stress of the electric fieldlight emitting layer 6011, and the reliability is thus enhanced.

In the example shown in FIG. 41, a positive photosensitive acrylic resinis used for the organic resin film 6014. Photosensitive organic resinsare classified into a positive type and a negative type. A part of aresin that is exposed to an energy beam such as light, electron, and ionis removed if the resin is the positive type and is left if the resin isthe negative type. A negative type organic resin film too can be used inthe present invention. Also, the organic resin film 6014 may be formedfrom photosensitive polyimide.

When a negative acrylic resin is used to form the organic resin film6014, the end of the organic resin film in the opening 6015 is shapedlike the letter S in section. The radius of curvature thereof at theupper edge and lower edge of the opening is desirably 0.2 to 2 μm.

The anode 6010 may be formed from a transparent conductive film. An ITOfilm as well as a transparent conductive film obtained by mixing 2 to20% of zinc oxide (ZnO) with indium oxide can be employed. In FIG. 41,ITO is used for the anode 6010. The anode 6010 may be polished by CMP ora porous polyvinyl alcohol-based substance (Bellclean washing) in orderto level its surface. The surface of the anode 6010 which has receivedpolishing by CMP may be subjected to ultraviolet irradiation or oxygenplasma treatment.

The cathode 6012 can be formed from other known material as long as itis a conductive film having a small work function. For instance, Ca, Al,CaF, MgAg, AlLi, and the like are desirable.

In the structure shown in FIG. 41, light from the light emitting elementis emitted toward the substrate 6000 side. However, the light emittingelement may be structured such that emitted light travels in thedirection opposite to the substrate.

In FIG. 41, the transistor 6002 is connected to the anode 6010 of thelight emitting element. However, the present invention is not limitedthereto and the transistor 6002 may be connected to the cathode 6001 ofthe light emitting element. In this case, the cathode is formed on thethird interlayer insulating film 6008 from TiN or the like.

In practice, it is preferable to package (seal) the device that hasreached the stage of FIG. 41 with a protective film which is highlyairtight and which allows little gas to leak (a laminate film, aUV-curable resin film, or the like) or a light-transmissive cover memberin order to avoid exposure to the outside air. In packaging the device,the interior of the cover member may be set to inert atmosphere or ahygroscopic material (such as barium oxide) may be put inside in orderto improve the reliability of the device.

The present invention is not limited to the manufacturing methoddescribed above, and the device can be manufactured using a knownmethod. This embodiment can be combined freely with Embodiments 1through 13.

The present invention runs laser light so as to obtain at least theminimum degree of crystallization of a portion that has to becrystallized, instead of irradiating the entire semiconductor film withlaser light. With the above structure, time for laser irradiation ofportions that are removed by patterning after crystallization of thesemiconductor film can be saved to greatly shorten the processing timeper substrate.

Furthermore, the crystallinity of a semiconductor film can be enhancedmore efficiently by overlapping plural laser beams to compensate oneanother's low energy density portions compared to the case where laserbeams are not overlapped and a single laser beam is used.

Although the description given in the present invention is about thecase where laser light emitted from plural laser oscillation apparatusesare synthesized, the present invention is not particularly limitedthereto. The present invention may use only one laser oscillationapparatus if it has relatively high output energy and is capable ofproviding a desired energy density without reducing the area of its beamspot. In this case also, the use of a slit makes it possible to blocklow energy density portions of laser light and to control the beam spotwidth in accordance with pattern information.

1. A laser irradiation method comprising: determining, from patterninformation of a sub-island obtained by patterning a semiconductor filmformed over a substrate, a specific region on the substrate that is tobe irradiated with laser light, the region including the sub-island;using an optical system to partially overlap beam spots of plural laserlights that are outputted from plural laser oscillation apparatuses toform one beam spot; using a slit to reduce a width in a directionperpendicular to a scanning direction of the beam spot formed; runningthe beam spot with the reduced width over the specific region to enhancecrystallinity of the sub-island wherein the sub-island is included in anarea irradiated in the reduced width by the running of the beam spot;and patterning the sub-island with enhanced crystallinity to form anisland.
 2. A laser irradiation method according to claim 1, whereinlaser light irradiation takes place in a reduced pressure atmosphere orinert gas atmosphere.
 3. A laser irradiation method according to claim1, wherein the laser light is outputted from one or more kinds of lasersselected from the group consisting of a YAG laser, a YVO₄ laser, a YLFlaser, a YAlO₃ laser, a glass laser, a ruby laser, an alexandrite laser,a Ti:sapphire laser, and a Y₂O₃ laser.
 4. A laser irradiation methodaccording to claim 1, wherein the laser light is continuous wave laserlight.
 5. A laser irradiation method according to claim 1, wherein thenumber of the laser oscillation apparatuses is equal to or more than 2and equal to or less than
 8. 6. A laser irradiation method comprising:determining, from pattern information of a sub-island obtained bypatterning a semiconductor film formed over a substrate, a specificregion on the substrate that is to be irradiated with laser light, theregion including the sub-island; using an optical system to partiallyoverlap beam spots of plural laser lights that are outputted from plurallaser oscillation apparatuses so that centers draw a straight line toform one beam spot; using a slit to reduce a width in a directionperpendicular to a scanning direction of the beam spot formed; runningthe beam spot with the reduced width over the specific region to enhancecrystallinity of the sub-island wherein the sub-island is included in anarea irradiated in the reduced width by the running of the beam spot;and patterning the sub-island with enhanced crystallinity to form anisland.
 7. A laser irradiation method according to claim 6, whereinlaser light irradiation takes place in a reduced pressure atmosphere orinert gas atmosphere.
 8. A laser irradiation method according to claim6, wherein the laser light is outputted from one or more kinds of lasersselected from the group consisting of a YAG laser, a YVO₄ laser, a YLFlaser, a YAlO₃ laser, a glass laser, a ruby laser, an alexandrite laser,a Ti:sapphire laser, and a Y₂O₃ laser.
 9. A laser irradiation methodaccording to claim 6, wherein the laser light is second harmonic.
 10. Alaser irradiation method according to claim 6, wherein the number of thelaser oscillation apparatuses is equal to or more than 2 and equal to orless than
 8. 11. A laser irradiation method comprising: patterning asemiconductor film formed over a substrate to form a sub-island using amask; detecting pattern information of the sub-island using a CCD;grasping a position of the substrate by checking pattern information ofthe mask against the detected pattern information of the sub-island;determining, from the pattern information of the sub-island, a specificregion on the substrate that is to be irradiated with a laser beam spot,the region including the sub-island; using an optical system topartially overlap beam spots of plural laser lights that are outputtedfrom plural laser oscillation apparatuses to form one beam spot as thelaser beam spot; using a slit to reduce a width in a directionperpendicular to a scanning direction of the beam spot formed; runningthe beam spot with the reduced width over the specific region to enhancecrystallinity of the sub-island wherein the sub-island is included in anarea irradiated in the reduced width by the running of the beam spot;and patterning the sub-island with enhanced crystallinity to form anisland.
 12. A laser irradiation method according to claim 11, whereinlaser light irradiation takes place in a reduced pressure atmosphere orinert gas atmosphere.
 13. A laser irradiation method according to claim11, wherein at least one of the plural laser oscillation apparatuses isselected from the group consisting of a YAG laser, a YVO₄ laser, a YLFlaser, a YAlO₃ laser, a glass laser, a ruby laser, an alexandrite laser,a Ti:sapphire laser, and a Y₂O₃ laser.
 14. A laser irradiation methodaccording to claim 11, wherein the laser lights are continuous wavelaser lights.
 15. A laser irradiation method according to claim 11,wherein the number of the laser oscillation apparatuses is equal to ormore than 2 and equal to or less than
 8. 16. A laser irradiation methodcomprising: patterning a semiconductor film formed over a substrate toform a sub-island using a mask; detecting pattern information of thesub-island using a CCD; grasping a position of the substrate by checkingpattern information of the mask against the detected pattern informationof the sub-island; determining, from the pattern information of thesub-island, a specific region on the substrate that is to be irradiatedwith a laser beam spot, the region including the sub-island; using anoptical system to partially overlap beam spots of plural laser lightsthat are outputted from plural laser oscillation apparatuses so thatcenters draw a straight line to form one beam spot as the laser beamspot; using a slit to reduce a width in a direction perpendicular to ascanning direction of the beam spot formed; running the beam spot withthe reduced width over the specific region to enhance crystallinity ofthe sub-island wherein the sub-island is included in an area irradiatedin the reduced width by the running of the beam spot; and patterning thesub-island with enhanced crystallinity to form an island.
 17. A laserirradiation method according to claim 16, wherein laser lightirradiation takes place in a reduced pressure atmosphere or inert gasatmosphere.
 18. A laser irradiation method according to claim 16,wherein at least one of the plural laser oscillation apparatuses isselected from the group consisting of a YAG laser, a YVO₄ laser, a YLFlaser, a YAlO₃ laser, a glass laser, a ruby laser, an alexandrite laser,a Ti:sapphire laser, and a Y₂O₃ laser.
 19. A laser irradiation methodaccording to claim 16, wherein the laser lights are second harmonic. 20.A laser irradiation method according to claim 16, wherein the number ofthe laser oscillation apparatuses is equal to or more than 2 and equalto or less than
 8. 21. A laser irradiation method comprising:determining, from pattern information of a sub-island obtained bypatterning a semiconductor film formed over a substrate with a marker asthe reference, a specific region on the substrate that is to beirradiated with laser light, the region including the sub-island; usingan optical system to partially overlap beam spots of plural laser lightsthat are outputted from plural laser oscillation apparatuses to form onebeam spot; using a slit to reduce a width in a direction perpendicularto a scanning direction of the beam spot formed; running the beam spotwith the reduced width over the specific region to enhance crystallinityof the sub-island wherein the sub-island is included in an areairradiated in the reduced width by the running of the beam spot; andpatterning the sub-island with enhanced crystallinity to form an island.22. A laser irradiation method comprising: determining, from patterninformation of the sub-island obtained by patterning a semiconductorfilm formed over a substrate with the marker as the reference, aspecific region on the substrate that is to be irradiated with laserlight, the region including the sub-island; using an optical system topartially overlap beam spots of plural laser lights that are outputtedfrom plural laser oscillation apparatuses so that centers draw straightlines to form one beam spot; using a slit to reduce the width in thedirection perpendicular to the scanning direction of the beam spotformed; running the beam spot with the reduced width over the specificregion to enhance crystallinity of the sub-island wherein the sub-islandis included in an area irradiated in the reduced width by the running ofthe beam spot; and patterning the sub-island with enhanced crystallinityto form an island.
 23. A laser irradiation method according to claim 21,wherein the straight lines the centers draw are at angles of 10° orlarger and 80° or less with the direction in which the substrate moves.24. A laser irradiation method according to claim 22, wherein thestraight lines the centers draw are at angles of 10° or larger and 80°or less with the direction in which the substrate moves.
 25. A laserirradiation method according to claim 21, wherein the straight lines thecenters draw are almost at right angles with the direction in which thesubstrate moves.
 26. A laser irradiation method according to claim 22,wherein the straight lines the centers draw are almost at right angleswith the direction in which the substrate moves.
 27. A laser irradiationmethod according to claim 21, wherein laser light irradiation takesplace in a reduced pressure atmosphere or inert gas atmosphere.
 28. Alaser irradiation method according to claim 22, wherein laser lightirradiation takes place in a reduced pressure atmosphere or inert gasatmosphere.
 29. A laser irradiation method according to claim 21,wherein the laser light is outputted from one or more kinds of lasersselected from the group consisting of a YAG laser, a YVO₄ laser, a YLFlaser, a YAlO₃ laser, a glass laser, a ruby laser, an alexandrite laser,a Ti:sapphire laser, and a Y₂O₃ laser.
 30. A laser irradiation methodaccording to claim 22, wherein the laser light is outputted from one ormore kinds of lasers selected from the group consisting of a YAG laser,a YVO₄ laser, a YLF laser, a YAlO₃ laser, a glass laser, a ruby laser,an alexandrite laser, a Ti:sapphire laser, and a Y₂O₃ laser.
 31. A laserirradiation method according to claim 21, wherein the laser light iscontinuous wave laser light.
 32. A laser irradiation method according toclaim 22, wherein the laser light is second harmonic.
 33. A laserirradiation method according to claim 21, wherein the number of thelaser oscillation apparatuses is equal to or more than 2 and equal to orless than
 8. 34. A laser irradiation method according to claim 22,wherein the number of the laser oscillation apparatuses is equal to ormore than 2 and equal to or less than 8.